Few points:
1) This will be a nightmare if the sensor response times aren't absolute perfection. Nothing, and I repeat
nothing is more frustrating to a rhythm gamer, casual or serious, than poor judgments caused by some type of latency or inconsistency with the game (or associated hardware) itself.
2) The AR aspect of using your camera while playing is a bit lost on me. The reason you gave is that you can record your friends while you're playing the game, but I don't understand why you would want to do that. The only tie-in I can find for why you would want AR on a game like this is that if the person controlling the phone is given dance moves, the friend they are recording on AR must mimic those moves and be scored accordingly on the app (Sort of like a just dance vibe, but the person you're recording mimic's your moves instead of the cartoons on the screen).
3) Look and feel: Long way from where it needs to be. I'm reminded of low-quality DDR knockoff games like
this one which is definitely not a good thing when you're competing with things like
Deemo or even other mobile rhythm games that track your movement like Just Dance Now.
4) As stated by others, Unity is not a great platform for rhythm games. It has been tried before and people now know to avoid it because of how laggy it can be.