I have always loved skydiving games and I know there is a large community that does too. So what about a 3D top-down skydiving game, where you control your flight in a large world, pull your chute, and fly into a designated area. With each level beaten, you unlock another level, a bit more challenging. The levels could go from plane jumps to heli jumps and even to BASE jumps. There are so many different possibilities for variety here I think it would do well in the app store.