Main things I'm interested in are:
1) Real time segments. Get alerts whilst riding of segments and also segment scores in real time.
2) Sufferfest videos for indoor training over winter.
3) Suffer score/heart rate zone analysis (I know this is free elsewhere but all my friends are on Strava so it's easier to use this).
4) Support Strava. Been using their free app for sometime. I'd like to help them improve their service.