Is there anything that the "remote control" has that really needs to be integrated into a "shell"?
The only thing I can see it reusing would be the remote's transmitter. That's it.
In other words, the shell will have to have it's own:
1. Casing
2. Buttons, triggers, sticks, pads.
3. PCB for the aforementioned parts
After you've gone through all of the trouble and designing and producing such a thing, does it really make sense to design a special slot to incorporate the remote? Why not just go the extra millimeter and make the "shell" a standalone controller?
In fact, if Nintendo were really smart (it's questionable), they would incorporate yet another flashback to the past with the system and ship it with all three controllers:
--Remote
--nunchuck
--gamepad
That used to be the way things were done. You bought a system, and you got joysticks and paddles, or controllers and light guns, or 3D glasses, light guns, and controllers, or ROB, Power Pad, Zapper, Control Pad, and rainbow flag decal.
The end.