It was suggested recently that the initial character creator should have some default poses so users can get a feel for what their character looks like in action. Perhaps a few default animations could be provided as well, even if they are just idles or walks. Seeing the character you just made start moving naturalistically would be amazing.
I have also been wondering about the possibility of Y2 allowing you to animate transformations in the characters beyond just inflation, such as changes in size, muscle mass, colour, etc. I have no idea if this would be feasible though, I just know that a lot of people like seeing their characters change.
My other suggestion is to focus on giving the models good eyes. They are the secret to a convincing character and if they look dead the whole scene loses something. Unity has addons that generate natural seeming eye movement, perhaps you could take inspiration from that. 'My eyes are up here' jokes aside, users are going to be looking at them an awful lot and they'll want to see life behind them.