Switch software is doing stupidly well, so I think there'll be plenty of 10m sellers.
My guess would be:
Already There:
Mario Odyssey
Mario Kart 8 DX
Zelda
Pokemon LG E/P
Smash
Released/Announced stuff that will make it:
Splatoon 2
Animal Crossing
Pokemon Gen 8
Stuff that can make it, if marketed properly/recieved really well:
Dragon Quest XI S
Super Mario Party (provided that no sequel is released)
Stuff that is likely in the works that would make it:
Pokemon Gen IV remakes
Pokemon Gen 8 third game/sequel
Pokemon Gen 9
Zelda BOTW sequel
3D Mario
Super Mario Maker
I'm likely forgetting a few big hitters that have a chance, but these are my guesses.