It’d be cool if model creators (and casual players) could add their own model-specific animations or features when importing a model. Of course, all of these would be added in Blender beforehand and would need to be quality-checked for any decreases in other players’ performances.
Adding this would give player models new life and would make things a more personalized feel for each person you run into. Maybe even a way to import animations to existing models (Thought I can see how this could be abused, but that’s where reporting comes in handy).
A by-product of this feature would also be adding actual physics to the models that already exist. Dresses that actually flow, tails that actually move, and ears that can react to head movements.
Basically any change to the customization that’s already in the game would be a great update no matter what, but why not just go big and give creators that extra bit of freedom?
EDIT: I’m adding this to the suggestion post as a whole because it completely slipped my mind until someone said it in the replies, but blinking eyes would also add a ton to the models.