I don't think anything will be able to hold AC down. It's been incredible, so many people I know who had zero interest in games have fought to buy a Switch just to play it. It's momentum has been sustained as well.
My predictions:
1. Animal Crossing NH 21m
2. Pokemon Sw/Sh 19m
3. Zelda BOTW 18.5m
4 Mario Odyssey 18.3m