Personally I dont care about more body options at all. I utterly fail to see the gain.
Immersion and diversity aside, there are even some practical ones. Having normal or thin body while ALSO being tall (which is currently impossible) would provide a better scenes for romance with Karlach, for example
Immersion to me is a term that gets brutally abused all the time in gaming forums. A game has good immersion if it has good game mechanics. Thats the only trick to actually immerse people in a game. Thats why a game like chess has such extreme immersion.
Realism isnt one, unless lack of realism breaks your suspension of disbelief. The Tiefling and Githyanki both break my suspension of disbelief, for example, thats why I'm annoyed about them. No point in complaining though because neither will go away (or rather, made more realistic, like I would much prefer them), so whatever.
