It think it's Pokemon. Pokemon has a very loyal fanbase of players who don't play almost anything other than Pokemon. It has potential to move easily from 15 to 20 million hardware units
No system with Pokemon ever sold less than 70 million units. The game even gave Game Boy an entirely new sales run, Pokemon is that big
In second place, I will be controversial and say it's Animal Crossing. I might be wrong but I feel after New Horizons it cultivated a following of Animal Crossing players, not exactly Nintendo fans, but Animal Crossing fans. Hardware numbers for next game will be huge, mark my words







