In my opinion if sliders are not an option we should have 4 body types.
It would not impact the current armor models too much but it would really help with immersion.
Muscular, Athletic, Average and Plump.
I don't think Muscular should look like the hulk and neither do I think Plump should be obese. I don't think Larian has the budget to model every single piece of gear to so much variety.
But as long as it's somewhat noticeable and within the theme of the game then its alright.
They're already having to deal with animation collisions of the different heights and builds of the different races. Adding in some size options (thin, tone, muscular, overweight) would be appreciated. It might make the intercharacter animations difficult, though. That sex scene was already buggy.
Not really these body-types would mostly be abs, guts, shoulder, thigh and upper arm changes. I don't think you should be able to have giant muscular humans. The current model is fine, just give them a bit more muscle (or less in some cases)
The animations should still work with no problems.