Another half baked puzzling decision. This "mirrors" on what we have for DOS2 basically. Actually, it was way more flexible in DOS2, as you can change your companion's looks.
They are probably working on this and ran into bugs. Imho the functionality to change race can't be too different from the disguise self spell. But it's hard to say without knowing how they coded it.
I dont think it's fair to compare dos2 mirror functionality. Your race only affected dialog options. Bg3 race determines dialog options AND cutscenes.
Wyll and shadowheart models are clearly the main problem with customizing origin characters, without going into spoilers.