10 million is honestly like, no work at all. With zero marketing at all, There were at minimum 10 million BotW fans who are all-in on a direct sequel (myself included).
Hitting 20 million, or heaven forbid the holy grail of 25 mil or 30 mil for a direct sequel, in the late stage of a console lifecycle, on a single platform, that’s the real open question.
It’s possible, but it seems like the game will settle out on Switch around 15-20 mil.
If they re-release it as an upgraded port for new hardware, it’ll absolutely exceed OG BotW sales.