The main issue I would see with fat bodies isn't animation, likely you could still use the same rigs and just accept some clipping as a fact of life, but that the textures/models for all of the armor would need to be redone. As otherwise the only 'fast' solution is just stretching which will look terrible for much equipment, and otherwise just require more work. Considering all of the problems that the game has, especially Act 3 being a veritable open beta, the need for fat bodies kinda feels like something to touch on as the last thing on the list for a definitive edition.
Also customization in the game is barebones as hell so I don't really see how the lack of beer bellies sticks out either, you only get a handful of face structures and can't even tweak them. It's more that character customization is overall very bare bones for the player model. Things like jaw width, chin pronouncement, cheekbones, etc, usual sliders in many RPG's just aren't here. Considering how rare weight sliders are in RPG's it's of little surprise it's not in either.
