Aside from the ones that reached or are set to reach it, I think Animal Crossing, Mario Tennis and Metroid Prime 4 both have a good chance, and Fire Emblem definitely will smash (no pun intended) previous entries numbers.

Pokémon also have a good chance... it all depends on legs. But since Pokémon games will take more time to launch in between them, I think this one has a good shot. 15m+ first quarter is my modest guess.

EDIT: Forgot about Smash. It's totally outselling the previous entries, and I bet it will achieve it on the first year on top of that. Mark my words. PS: If it's a new game, of course.

Metroid, Mario Football, Mario tennis, Fire emblem and Yoshi.

probably pokemon, they have a color and or (insert item here) edition every release, and many of the pokemon faithful will buy all 2 or 3 versions at the same time boosting numbers. thought its a high number to break, the switch seems to be right for big nintendo titles getting big numbers.

if not that would be surprising, maybe a new smash bros would peak on switch.

for me new mario kart, and a new 2d mario is something i would be stoked for, we have to see if a new one of either of these titles will come out at all.

Mario odyssey is still behind galaxy one that shipped 12.75m, so it is not the best selling 3d mario yet although it will be in a few months.

I would say that evry Nintendo IP can peak on Switch except Mario Kart (maybe if Switch start bundleing MK8D hard), 2D Mario and Donkey Kong Country.