Mario
Possibly Probable: Bowser Jr. is an incredibly popular device that Miyamoto likes to shove into just about ever Mario IP recently. If there's any new Mario main series character at all, it's definitely going to be him. Less likely, but possible due to the nature of having a seperate Dr Mario character in Melee is the Paper Mario incarnation. His newest game was recently released, seems like it could be a good tie-in.
Selfish Desires: I've always wanted to see just about any major RPG subseries character who wasn't frequently seen in the main series. My top three are Fawful, Geno and Smithy. Fawful has a lot of interesting gadgets, Geno is a hero who can transform in a number of ways and would look cool with a modern redesign, but Smithy is GENUINELY a selfish, selfish idea because there's already a heavy character who wields a hammer and is a villain, and unlike Smithy he's not owned by Square and virtually impossible to acquire. Actually, I'd even settle for a lazy reskin of Dedede to make Smithy a character. I'm that shallow.
Inkling Fears: If alternate costumes is not a viable idea, I may never get to see Dry Bowser in a playable Smash Bros form.
Zelda
Possibly Probable: Ghirahim feels like the most likely new Zelda character. He's an enjoyable villain who's NOT Ganondorf, he's from the latest Zelda game, and he's a villain character who's NOT insanely slow and heavy.
Another less likely, but POSSIBLE note for consideration is the Skull Kid from Majora's Mask. At first this idea wasn't really that timely. However, there is a Wii U remake of Majora's Mask coming out. Suddenly it's MUCH more timely. At the very least they've got to consider including a nice new MM stage. Nevermind that trailer was a hoax NNGGGGGGGGGGGGG
Selfish Desires: I've always wanted Ganon as a fully playable character in some way. Not just Ganondorf's Final Smash, but a legit pig Ganon as a playable character. They haven't completely abandoned him, after all. He's in Nintendo Land, albeit that's a poor example to use because of it being so stylized and incredibly big. Still, that's what I want. So bad. Oh, and I'd LOVE to see an Agahnim alternate costume for Ganondorf, although the more logical choice would be the ability to choose either OoT or TP. I still kind of wish he was his own character too, and able to use a sword. Almost every design had swords involved at one point (though for the OoT design you really have to stretch it. It was never in a game really).
I'd also like to see the Toon Zelda concept realized. A lot of people speculated that Toon Zelda would have the traditional Zelda/Shiek mechanic, but with Tetra instead of Shiek. Tetra's one of my more favorite characters from the Wind Waker style of Zelda games. Plus that version of Zelda was the first one to ACTUALLY use Light Arrows. That's a minor point though overall.
Inkling Fears: Zelda was redesigned for Skyward Sword, so it begs the question what design they would use for Smash Brothers. However, the problem is that, as far as I know, there was no Shiek equivalent in Skyward Sword. Would they design a totally new equivalent, keep the old Zelda as a playable, or scrap the Shiek concept all together? I feel like this is something that's already been brought up or thought of in the actual development of the game, but who knows, maybe it's already a solved problem.
Yoshi
Possibly Probable: As mentioned in the Smash article in the OP, there's rumors of there being a partner in the new Yoshi game being developed. If this is true, that's an easy tie-in to make. It also expands the Yoshi games in Smash Bros without over-developing the Mario games, if you can forgive that it's a spin-off.
Selfish Desires: I've always wanted Shy Guy to be kind of a joke character, or even a real character. They have an extensive arsenal for suitable moves, and even options for different costumes. I also have always wanted a Kamek assist trophy. He'd make the user big and the enemies small. This might actually be more likely considering his presence in the main Mario games now. Also if they consider making more cloned characters, one clone I WOULDN'T mind seeing so much is Birdo as a clone of Yoshi. Birdo needs more love.
Inkling Fears: None really, Yoshi's always been an odd subject for me when it comes to Smash Bros. Really he could be considered an extension of the Mario universe, so I don't know how much extra characters his game series would merit.
Wario
Possibly Probable: Waluigi, while technically not a staple in the actual Wario Series of games, clearly wouldn't exist without Wario existing, so I'm just lumping him in here. A representative of the casual party games and sports games that the Mario series has to offer, it allows much of the sports games to be represented through him in some way with his moves. He was pretty much the poster boy for the concept of an Assist Trophy, so it is clear there was at least some interest to have him in the game. That's pretty much the idea of Assist Trophies in the first place.
Selfish Desires: Captain Syrup. Get a legit pirate into Smash Bros.
Inkling Fears: Getting no Waluigi and leaving Wario all on his greedy lonesome.
Kirby
Possibly Probable: Sakurai, at least from what I remember reading, feels awkward about putting his own characters ahead of anyone else's, thus eliminating the possibility of including Meta Knight or Dedede in Melee due to time or resources restraints or whatever it was. For that reason it might be unlikely to see a new Kirby character. However, if there was one, Knuckle Joe seemed to be the most popular candidate seeing as he was an Assist Trophy, or even Waddle Dee as he was seen in Return to Dreamland.
Selfish Desires: I've always wanted a LEGIT villain in Smash. Dedede has always been more of a brush-off villain since his initial debut. Sure, he's strong, he's mean, but he's rarely the TRUE villain. I'm pretty much Marx's biggest fan, but Return to Dreamland's main villain seems more timely, and I'd settle for that too. Other than that, I've got a soft spot for Daroach as well. At least include him and the Squeaks as background fodder if they can't be worked in some other way.
Inkling Fears: Kirby is one of my favorite series of all time. If there was no real Kirby reps added this time around I'd be disappointed.
I'd also understand if there weren't though for afforementioned reasons.
Metroid
Possibly Probable: The article mentions Ridley, and even if the article is bogus he's still the most sought-after Metroid villain to be included. He's by far the most iconic, making more appearances than any other Metroid villain to date. In fact, he's probably made more appearances than ANY metroid character other than Samus or the Metroids themselves. However, I didn't like the design of Other M's Ridley, mainly his head for some reason. However, any Ridley's better than no Ridley.
Selfish Desires: Although not a commercial success, I've always wanted another bounty hunter from Metroid Prime: Hunters. Sylux has always been my top pick. Sort of the evil version of Samus; has his own ship, spits in the Federation's face instead of working with them, but still totally badass like Samus. I've also always had a soft spot for Dark Samus, despite just being a more evil-looking Samus with some different abilities. Still, DS was the main villain of the entire Prime series. Also, Metroid Fusion costume pleeease. Lastly, I've always wanted the Baby Metroid (the one that becomes gigantic) from Super Metroid to be a rare assist trophy. Imagine it latching onto one or more of your enemies and sucking them up to 999% damage in a few seconds. That would be such a devastating feeling.
Inkling Fears: No Ridley, or no new Metroid rep at all. Metroid's a far too awesome series to merit only one blip on the Character Select screen.
Pokemon
Possibly Probable: A difficult game to satisfy everyone since it is littered with HUNDREDS of monsters, but given its track record Zoroark is the most likely new addition. Whether or not he will be completely new as a character, replace Lucario, or both is just speculation at this point.
Selfish Desires: I really REALLY want Mewtwo back, and I want him MUCH stronger than in Melee. However, one character I almost want to see more than Mewtwo is N. Have N be an actual character, and have him call out Pokemon for certain strong and for special attacks. Lastly, I still want to see Meowth as a playable character, but that would expand the 1st gen representation in the game up yet again. Then again, the first one is what started it all. Oh, and Deoxys. He's just got an interesting concept and look.
Inkling Fears: No return of Mewtwo and trying to make a character that's even more awkward than the Pokemon Trainer.
Star Fox
Possibly Probable: It is very much possible that Star Fox may not get any new characters at all. Zelda went a generation of Smash Bros without really expanding its character line-up (Toon Link is just a remodeled Young Link, let's face it), so with three characters in the game who are already considered so similar, its likely the series might just stick with them. They kind of bring the series its Ryu/Ken/Akuma kind of character dynamic, so maybe its for the best.
Selfish Desires: First and foremost, just a BIT more differentiation between the three current characters, namely the Final Smashes. Have one of them pilot something else, PLEASE. The one character who I've ALWAYS wanted to see is Andross. Seems silly given the fact that he's almost always enormous, but it gives the development staff a chance to work their creative muscles. They could even get cheeky with it, mentioning that often Andross fights using some sort of robotic double, or something to that effect, and call out the fact that the Andross you play as may not actuall BE Andross. I just love monkeys as diabolical villains.. I don't know, it's a thing.
Inkling Fears: Not only keeping the triple Landmaster crap, but somehow making the three characters even MORE similar.
Donkey Kong
Possibly Probable: The fact they want to add K. Rool is only a rumor right now, but he IS often requested, and easily the most recognizable villain in the DK universe. Also, its a good way of introducing a comeback for the character for future DK games, which there definitely SHOULD be after DKC Returns.
Selfish Desires: If K. Rool gets in I'd really be set. However, a Cranky Kong joke character would make my life complete.
Inkling Fears: No new DK characters at all due to it not being considered the most important series of Nintendo games.
F-Zero
Possibly Probable: Samurai Goroh, being the only other F-Zero character to even appear in a gameplay context at all in the Smash Series, seems reasonable for the next character in line for a spot. If not him, Black Shadow is Captain Falcon's main villain, so his presence could be possible.
Selfish Desires: Tacking the slow and strong Captain Falcon clone gameplay of Ganondorf onto Black Shadow instead.
Inkling Fears: I don't really know enough about F-Zero to have any real fears here, but I do feel like Captain Falcon is too lonely to keep driving alone. Cut the guy a break.
Mother/Earthbound
Possibly Probable: At first I was going to say there's no way they'd even consider another Mother character given the fact the series is no longer as timely and that two out of three games are only released in Japan officially and that the only one that isn't is so rare you could spend more money on it than on a house. However, that was until I read
THIS article. The article could mean any number of things, but if it somehow makes the Mother series more playable to the world in general, it might be a great way to tie it into Smash Bros. That being said, a new character from the series could be possible, but at this point its impossible to determine which beyond speculation (though that's really ALL this is, so...)
Selfish Desires: Claus. Claus Claus Claus Claus Claus. And maybe Porky if they were being generous, with a helping of Giygas as a Final Smash or a stage.
Inkling Fears: Even worse than no new character at all would be having Ninten from Mother 1 be added and be almost the same as the first two boys (even though they are fundementally different and that I like Lucas a lot better).
Fire Emblem
Possibly Probable: Fire Emblem is a complicated beast. Up to this point it has mainly been used as a marketing tool, sans Marth that is. The second character slot has gone to a character who had a game recently released. That being said, I feel like Chrom is next in line, if there was any character added at all.
Selfish Desires: Fire Emblem, like Pokemon, has far too many characters to appease anyone. Lyn seems like a cool idea since she's both another girl character and she's from the first Fire Emblem game released outside of Japan. I'd really like a villain to be included though, something like either a super heavy armored general or an evil sorcerer. There are plenty that fit the bill (some that fit BOTH bills). The whole process gets overly complicated though when you consider that the 3DS Fire Emblem game is going to be including MANY of the characters from unreleased series in as Spot Pass or full Downloadable characters.
The MAIN wish I have though is to have Roy back, but adjust his moveset to incorporate the dual swords concept he seems to use for the 3DS title.
Inkling Fears: The weight of Fire Emblem's extensive roster just making them cave in, removing Ike and including Chrom, perhaps even with the exact same moveset.
Kid Icarus
Possibly Probable: With Kid Icarus: Uprising being mostly Sakurai's responsibility, it could go one of two ways. Either the presence of a new character for Smash becomes a priority, OR he push the opportunity for a new character from the series aside in order to include others from other series. The former seems more likely. The game is fun, one of the best 3DS titles around, full of character. That being said, the likelyhood of one character over another isn't that clear. The top three are Medusa, Hades and Palutena. Some might say Palutena's less likely because of her being in Pit's Final Smash, but anyone who's played Uprising knows that there are better things for Pit to use as a Final Smash now.
Selfish Desires: Magnus, Phosphora and Viridi all have pretty cool designs and concepts for abilities, but none of the three are really more deserving than the other three that were already mentioned. That being said, I'd love to see them as either assist trophies or in stage environments. The Reset Bomb stage from Uprising seems like it could be a cool Smash stage.
Inkling Fears: Pitoo as a clone character. (In reality, I wouldn't mind seeing him as a totally new character using the less traditional kind of weapons that were introduced in Uprising, but I wouldn't want him over any of the other characters I mentioned before).
As for the rest of the series, like Animal Crossing or Golden Sun, it would be pretty pointless to go through all of them at this point. The ones beforehand had at least SOME sort of sense to back up my arguments, but for everything else it would be entirely speculative, at least moreso than the rest has already been in the first place.