I think Nintendo should wait to see what Sony's going to bring out and copy them instead!  LOL.  Sorry, I couldn't resist.

I believe we'll see modest improvements.  My wish list includes location/orientation sensors that work without the bar, rechargable batteries that charge with your own movement and/or a power source, a grip on the underside of the unit and an analog trigger.  I'd also like to see the Wii 2 be able to handle more than four Wiimotes at a time.

Beyond that, it would be nice to have a mini screen similar to the Dreamcast with its VMU.  (I'm surprised no one's done something like that since.)

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