I wonder how comfortable it'd be if the controllers were split in the center and the resultant looked like dual nunchucks. You could join them by a cable and add motion detection too. Since the left and right hands are essentially now independent to move, the developers have a lot more creative freedom with movement controls.
Just imagine taking your normal 360 controller and split it along the center. Now add gyroscope/accelerometer and two tracking cameras/LEDs (just like the WiiMotes).