I can imagine the fighting that would happen with only the Gamepad is considered....1st? Am I right in assuming that it has to be 1st? The few games we played on the Wii U was co op so it wasnt too much of a problem. The competitive games...I can see it being an issue..
In Smash and Mario Kart whoever selects the multiplayer option first is player one.
Of course you then have games like NSMBU and Nintendoland where the GamePad player can have a different role completely. But in the came of say Nintendoland it encourages giving everyone a chance on the GamePad.