This'll sound strange, but the first thing that came to mind was Mario Party 10. I think they could come up with some interesting minigames incorporating the GamePad, and I also like some of the ideas introduced in Mario Party 9 and would like to see them expanded.
Except Mario Party 9 is widely considered the WORST Mario Party game (or at least the worst console Mario Party).
If they make Mario Party 10, they should go back to the basics of the original N64 trilogy. 20 coins to get a star. Coin, Happening, and Minigame bonus stars, and Bowser wrecking **** up. Although I
would like to play as my Mii in the main party mode, unlike in 8, where Miis were relegated to the "extra" minigames.
Speaking of Miis, they NEED to be in Smash Bros. Do it, Sakurai!