Over 10 million easily, provided that Nintendo gives it a big push (which they will, I'm sure). The original game sold four million copies at a time when the Wii U was already dead in the water (shame), so releasing Mario Maker 2 on a system that currently has nearly three times the users and is growing in popularity by about a million units a month guarantees that it will be a big success! Also, I think that word of mouth is going to catapault it even further!