That is a lot higher than I thought! Good for them. I checked a couple different sources for the PS3 version, and from what I can tell that version sold about 7m. That means the PS4 version is actually the more popular version. I am guessing that is because the PS4 is a more popular platform?
This sort of thing may signal what type of performance the biggest Wii U titles will do on the Switch, only more extreme considering how big a flop the Wii U was.
Mario Odyssey should do 20+ million. It has more to do with the fact that games just sell more now. The ceiling for 3D Mario was like 12 million before Odyssey. The ceiling for God Of War was 5 million before the PS4 game. Uncharted was 8 million before UC4. Zelda was 8 million before BotW. It keeps happening.
If a game is well recieved critically, it will sell better than any other in the series past. 2 million sales is the new 1 million.