Well Blizzard hasn't shown us a single hint yet (bastards) so nobody really knows. But it would be a big change and I'm going to say it seems unlikely. I think they would want to avoid things like being able to screw with all your sliders to make your character look hideous on purpose. Breaks immersion.
I think the conservative forecast would be: no sliders or subraces or anything, just better skeletons/animations and much higher res models.