BlackandMild, that is almost perfect, but I would expect Nintendo to make a design that does not require the Third Component to make the controller. It is a additional component that means something could get lost, or Broken.
However, the 3rd Component could be the Brains of the controller and also a potential pointer for Wii Games. And I suppose the Docking bay could have slots on the side to lock 2 separate middle pieces together for storage and charging.
Personally, I think it is more elegant to have the two controllers slide into each other and lock into place...and eliminate the need for the middle piece.
Other than that, that Mock Up is perfect. Now think about how the right side could be replaced with a Gamecube controller, or Nintendo 64 button layout, or Street Fighter Layout fairly cheaply. Now also imagine that the left part could be replaced with a bigger D-Pad or Control Stick or even Extra buttons or Rhythm games....or piano keys for a music game.