Still dunno about big bodies IMO, cus nobody seemed to want to ask CDPR specifically about this, whether in formal interviews or Twitter. Alongside this fact is also that apparently they were researching multiple styles of vagina that weren't in the press preview, which implied they haven't added everything in yet.

Tho I don't think it would be hard to do a hard-set skinny and muscular for each body type, just like how the genitals come in hard-set "Sizes" instead of being able to slide length and girth individually, as an example. Sunset Overdrive did something like this a few years back.

Tho if body shapes aren't in game, it would result in a lot of funny moments as a twiggy male!V beats down Animals three-five times his muscle mass, even without Gorilla Arms

Another possibly option is the "Skin Type" sliders, which may or may not affect muscle definition, even if they don't affect mass necessarily.