I mean, anything else aside, I don't think you have anything to worry about; the way the game works internally, I think 'overweight' models would actually have to be implemented as new races, with their own outfits modeled. Like how there's an entire separate model for gear when equipped by Roegadyn men or Hrothgar, or by lalafell. If you just tried to scale existing gear to 'overweight' body types, the modeling would likely get weird. You'd probably have to do new models for every piece of gear, nearly, and that's likely far more work than the devs are going to be able to put into a feature like that.

I actually don't mind having a bit more body diversity -- really, I don't mind anything that gives a little more variety in character models! -- but I don't think we're likely to get it here, just on technical grounds.