I would love to be able to have the textures of some NPC's. For example, it would be great if my Night Elf Priest's eyes were to glow like Tyrande's. I don't like how all males have golden eyes, since lore-wise that honestly only fits a Druid. Having a silvery trail emitting from them could be fun.
Another feature I'd love for new models other than the obvious texture overhauls, however, would be weight scalers and subrace options. Both could add great diversity to a character.