This would be helpful to people who have polygon limits in mind when model hunting and would be pretty cool to know as well. It could be listed in the model statistics. In my experience one of the top criteria for my model hunting is polygon count as I use models in real-time environments in video games, so optimization is key and would be great to know in advance before attempting to optimize models myself.
This is certainly an interesting idea and I'd love to see it in action, but I think a fundamental issue arises in the very nature of how models are submitted. Model submissions are typically ZIP files or other archives which can contain not only several different formats of the same model, but different parts of models as well (especially in a case like with modern Nintendo games where character faces can have a completely new object for different expressions) or submissions which are or border "Everything" packs. There's no efficient way to track all of it in an automated sense, especially when models have to be verified manually. The alternative is to list every model in that ZIP with their poly counts or just list the total poly count of all the models in the ZIP but those can both get messy real quick. There'd also then be the proposal of "Why not list texture sizes as well?" and other situational nuances.
Sans automation, this information would either have to be provided by the mod verifying the file or by the submitter (which would have to be verified anyway). Then every model on Models Resource that already exists would have to be re-checked and verified for poly counts etc. Too much work for too little gain.
TL;DR: I like the idea, but it isn't exactly feasible in a proper manner. Too much work for just a statistic. You're better off just optimising it yourself or using an asset library that already exists, if you're making a game.