They're gonna have to push real hard for Mario to outsell Splatoon.
IIRC, there is no console bundle with SMM, which is pretty dumb, and I think that alone means that it won't outsell Splatoon.
"Just for comparison Uncharted 4 was 20x bigger than Splatoon 2. This shows the huge difference between Sony's first-party games and Nintendo's first-party games."