Fire Emblem Musou
Before that, not sure.
I'll hold off on the switch and might buy Zelda on Wii U until Mario Kart 8 Deluxe or Splatoon 2 are out. Can't believe I'm buying a console and Mario Kart 8 (+DLC) again just to play arena battle mode, aah.
If they announce more cool account features (cloud saves? please?) or anything else, I might get swayed, but so far my backlog is humongous enough on Wii U.
I did however just pre-order 2 Joycon's, in case someone in my friend circle ends up buying one, so we can get into some 4-player shenanigans. If I had more friends that are up for local multiplayer, not lying, I'd probably be there day 1. Carrying this thing over to a friend's house for Mario Kart looks so easy now!! (and to be frank, I did that a few times with the Wii U, and it wasn't heavy or bad - but just bringing the tablet and a charger cable looks a billion times less complicated!).
Also, 4 player Bomberman...