Hey! I suggested this too in my thread stub "The Little Things"...check it out. I think it is a good idea and I think there are some other things that could be done with motion plus.
Jump
It needs a jump button.
This may seem non-essential...maybe it is. But if you ask me, with the addition of flying and motion plus functionality there is going to be a strong sense of freedom of motion. Jumping would complete this.
Jump! Jump! Jump! Jump! :)