Probably something that uses the Wii U tablet gimmick to help sell it. Can't say I'm excited.
Specifics of Nintendo games are always hard to predict. I foresee another 3D game that employs the camera on the tablet controller more than the tablet itself, which is pretty limited because it's like having a DS, only you can't see both screens at once, dividing the experience and making it essentially less intuitive. With the camera they can shape worlds according to people's emotions, etc. Many more possibilities that are unexplored, by Nintendo anyways.
No reason to think that. The Galaxy games had very little Wiimote implementation, I'm hoping this is the same for the next 3D Mario.
Zelda is the franchise where they use the console's gimmick to help sell it.