i have to imagine it would be the mario game. i'll guess super mario galaxy 3, and they'll have two screens at once - one guy playing on the handheld while the other guy plays on the console in a wizard-esque race to the end of some pre-selected levels.
I...don't know about that. I feel like they'd need something else to not have a sense of same-y-ness from Super Mario Maker and NSMBU (compared to Wii U). Maybe Zelda U? Perhaps Retro's game?