Is it possible to stream a movie to Apple TV (either wirelessly or via WiFi) from an iOS device, while having a separate UI on the iPhone/iPad? The UI could for instance, act to control what is playing on the Apple TV.
Apparently you can do it with AirPlay: http://www.apple.com/iphone/features/airplay.html
If this is something Apple is already providing than it can be a waste of time to develop it on your own, as they can reject it saying that it provides a duplicate functionality.