The return of scaling so that realistic or heroic proportions can be easily created.

A completely new skeleton with as little mesh distortion as possible when bending/twisting.

Better facial mesh design to allow for more realistic and natural expressions.

Gravity morphs. I am not expecting the moon, but being able to shift the appearance of weight distribution on the meatier areas (thighs, breasts, glutes) would be spiffy. Heck, even making it a mag system would be fine.

A base texture split into reusable parts designed more like maps you see in high end 3D. A displacement map for veins, minor muscles. A color map. A bump map. A specularity map. etc.

A transparent shell for an eye material that covers the entire eye for easier spec/ref management.