Unlock a jersey in-game, get the opportunity to buy the physical version. e.g. New York or Innsbruck jerseys for recent examples. It would be really cool to capture that achievement outside of Zwift - plus all the hard work could get enshrined if we so choose - or wear the ■■■■ out of it in the real world. A take-away if you will.
Strava did this for a while in the early days when an event was completed. The California Triple Crown event does something similar once you complete the event.