How about motion feedback? For example, when a sword hits someting in the game, you feel a recoil-like movement. A robust version could be made with using 3 gyroscopes (one for each dimension) inside the controller (a bit like in powerball), but with current technology it would be very loud, power consuming and expensive. If there would be a virtual keyboard and fingers on screen which translates the movement of the fingers, there would be no need for physical keyboard.
Button wise, I think a good solution would be 4 buttons plus analog stick for thumbs and 3 pressure sensitive buttons for index finger, middle finger and ring finger. I have already a concept in my mind and I might draw it at some point.
EDIT: by the way, check out the Powerball World Record: http://www.youtube.com/watch?v=iXbax3wh99M
