There's a lot I'd like to see, but the only thing I can think of that hasn't been said by anyone yet that really NEEDS to happen is a new gosh dang Punch Out game. I don't know why this franchise isn't being milked harder, Punch Out on the Wii is one of the most solid overall games Nintendo has ever put out and that's saying something.
Beyond that, yeah I'd parrot new F-Zero, any proper Metroid sequel (Prime would be cool, 2D would be rad, better version of Other M's gameplay would be cool), Bayo 3 (and maybe Wonderful 10...2, though that seems unlikely), and a big ol' 3D Pokemon game that actually lets you catch all the Pokemon without having to deal with that stupid TRADING NONSENSE would be good. I would say a new Smash, but if they're going to do that I really don't want Sakurai to be in charge of it. If they're going to keep the same team and philosophy then I'd rather they just port Sm4sh and give us another wave of new characters. Also hoping for more 3rd party stuff. A KH3 port would be cool but is very unlikely. More indie games showing up, that'd be good.
Maybe a Star Fox game that doesn't suck and has an original story that isn't just another trite rehash of 64? Nah, probably impossible. Also I feel like a really visually intense Ping Pong sim would work great with them joycons. I'd say another Paper Mario game but they keep making bad ones so maybe it'd be better that they just stop altogether.
Also yeah, this, why are we not all pushing this more? I can hear it now.
*woosh* *Mario coin noise* *CAPCOM PRESENTS* *Nin-tendo!*
Gonna take you for a ride in-goddamn-deed. I mean we got Ryu and Mega Man in Sm4sh, anything is possible. They could even do a X Tekken thing and have canon team-ups. I have a feeling Arthur from Ghosts n Goblins would get along well with Luigi. You could have some representation of the protagonist from Dragon's Dogma have an in-game rivalry with Bowser, or Ridley. Story mode opens in a boxing arena and it's the match of the century, LITTLE MAC vs DUDLEY. "Hey Mac, watch out for Dudley's Corkscrew Blow, it'll open you up like a bottle of wine, baby, ha ha!" "You know what I say Mac, if you're throwing me a flower, it had better be a chocolate bar, heph heph heph."
These ideas are free Nintendo just do it.