hmm maybe something small in a non split screen third person co-op game (very specific I know
). When you get in a vehicle the player controlling the car would be driving on the tv and have a map displayed on his controller to navigate with, while the person controlling a turret on the vehicle would have the option of looking at his controller for a first person view for better accuracy. Physically moving the controller to move the turret around. This way both players can hold a new controller but only 1 of them has heavy data streamed to it, as a concern atm is whether or not the console can stream full games to 2 controllers.
Thats actually the only thing I can come up with so far thats not been shown by Nintendo already.
The guys making Battlefield 3 have actually made a suggestion for such an idea for battlefield 3 if it were on Wii U.
Something about one player controlling a vehicle while the other is controlling the vehicle's turret on the controller screen.
It would be great if they did such things for a Wii U BF3 version (which I think is likely even if it comes months after the other versions).