The resource cost implications of supporting multiple phenotypes in player characters will vary from one game to another, depending on the exact features the game supports.
It is sometimes possible to use simple limited scale factors for character height and radial width without making the clothing system look wonky, but it tends to be more difficult if you have major bodyshape alterations, as each piece of clothing typically needs a new version for each new bodyshape.
Layered clothing just adds to the complexity, of course, and imagine the possible effect on all those complicated multi-character animations in BG3 if the player's body parts are not quite where they are expected to be...
As it stands, I believe there are theoretically 18 bodyshapes from the 9 races ( ignoring sub-race differences ) each with 2 genders that players can pick from, although several races seem to share the human bodyshapes, so relaistically, there are probably 12 distinct "average" bodyshapes.
If you added bodyshapes for "skinny", "plump", "weedy" and "buff" for each race/gender combo, you would have 60 different bodyshapes which every wearable item would need to be tuned for, and every animation would need to consider. It is unlikely this would be practical before the August release window, unless this is a feature they already have that is not in EA.
Maybe if enough players express interest it might be a post-launch addition, since Larian have a decent reputation for enhancing their games.
