A few months back I remember noting that Rocket League would be right at home on Nintendo's new system, and sure enough it was confirmed at E3.

What as-yet-unannounced third party games do you think would be good candidates for Switch porting?

Overwatch

Persona 5, Metal Gear Solid V: The Phantom Pain, DragonBall FighterZ, Dead Cells, Dark Souls III, Code Vein.

With Nintendo skin DLC pack.

Donkey Kong instead of Winston
Samus instead of Pharah
Luigi instead of Lucio
Bowser instead of Reinhardt

Etc.

This would sell soooo... soo many copies.

We saw how well the "nintendo pack" made Minecraft sell on Wii U and how well its doing so far on Switch because of it.

Yeah this is the first one to come to mind for me too, it's a natural fit and could sell very well.

Any third party games really. I'm sure an audience can be found with any game, and having it on the go would make it more appealing. I'd be happy with fighters and RPGs at the very least.

Any multiplayer focused game.

Persona 5
Star Ocean
Overwatch
Monster Hunter Worlds
Yakuza
Kingdom Hearts 3

Metal Gear Solid 5

Dark Souls 3

Code Vein 

Dragon Ball Fighter Z

All of them.

Mostly or all the JRPGs.
- Overwatch
- Sims 4
- Simscity ot City Skyline (probably cant handle it)
- Plants vz Zombies garden warfare
- MH World