Could there be an in-saddle / out-of-saddle control for the avatar, controlled by one’s webcam?
I.e. Zwift-app scans your webcam (possibly by the user being able to draw a box around himself and the bike) and when the rider stands up, the avatar stands up as well. Bonus feature would be if the webcam can recognise when riding in the drops.
This should probably only be a cosmetic function, but it would be nice to see the avatar mimick the riders movements IRL.