They could 2DS Wii U by removing the GamePad, sell it for $250/$200, make the system interface not require the GamePad (obviously), patch all their games (or at least in reprints add a GamePad Required" label) to allow non-GamePad use, and call it Wii 2. Also remove Wii BC (those who want Wii BC and a GamePad in the box can still buy Wii U), and beef up the CPU (which is Broadway IIRC beefed up mainly for Wii BC) to help with better PS360 ports, but this is optional, so maybe not to allow Wii U to still play later games.
Here's a list of changes or rebranding with "GamePad-Required labels:
Super Mario 3D World = Absolutely not needed, minor adjustments are doable
Game & Wario = Will need to be required
Nintendoland = Required
New Super Mario Bros U = Already is optional
Sonic Lost World = 99% optional, I think only Rhythm Wisp still needs it, a minor adjustment
Lego City Undercover = Can be made optional, just have the scanner be on the TV and use the control stick to look around, easy breezy.
Pikmin 3 = Obviously not needed, just look back in the prequels.
Wonderful 101 = They should be able to adjust the bits where you'd need to look in the screen, maybe make it a Picture-In-Picture mode of sorts in those buildings.
ZombiU = Hard to tell, I would think they could make it optional, but the GamePad is a big selling point (all the good it's done for it...), they can just make it optional but obviously keep the GamePad controls in.
Can't think of much else out right now.