I think that the problem in playing with more than 2 controllers is due to the stream of the game on both controllers. If the information, during multiplayer, for example, is kept to a minimum like in SSF4 3D, i doubt that even if 4 Wii U controllers, sharing that amount of data, will strain the console.
The real question only lies on those 4 player games like Mario Kart and SSB, for example, but even than we are supposing that there will be too much data to process given by 4 controllers. Because, if there`s no stream of any kind, it won`t matter if they are playing with this or that controller.








