I think they will be working on a new IP, they are going for an thrid person adventure game(wether horror based, or more action based, no idea, but I would say they would lean more in the "uncharted" side).And they are going realistic.In that, I mean that they are going as realistic as possible with the graphics.

Metroid Prime 4. They'll finally do what the Metroid fans have been asking for.

I love it. Let's seal it and send it to Nintendo.

Spoilers: They'll reach the bottom, and decide to climb again. We won't know if this game was a sequel or a prequel. It's genius.

Tch, what a normie suggestion.

Personally I think the Prime trilogy should be left as is. I'd prefer to see a new FPS Metroid trilogy. Maybe a game after Fusion, or between Super and Fusion...only good this time.

Open world Action game that pushes the Switch graphics!

Whatever they're working on I hope it's a brand new IP. New DKC and 3D Metroid are all well and good, but there's only so much they can do with those established series.

Barbeque Eating Simulator, obviously.

I feel like it's gonna be a New IP.

edit: Since I wasn't specific enough i'm gonna say a new 3D Action/Adventure IP. 

1-2 Switch: Switch It Up.

F-Zero

Apparently Nintendo asked them to make a new IP on WiiU but Retro told the they hadn't finished with DK yet and still had ideas, so along came TF. After seeing sales on Wii u, hopefully nintendo convinced them to make a new IP.