Prediction: Splatoon 2 will outsell Mario Odyssey lifetime.

[PAOerfulone]

Nope, not happening.

You can expect Animal Crossing type sales from Splatoon 2
Pretty good everywhere else; Absolute Monster in Japan.
As such, I would now expect around 12-13 million lifetime from it.

Mario, on the other hand, will be on another level.
Odyssey just had the best launch ever for a 3D Mario game in Japan.
https://gematsu.com/2017/11/media-create-sales-102317-102917
And with 2 million in its first week, right before the holiday season + overwhelming critical acclaim, expectations are now that Odyssey will become the best selling 3D Mario game of all-time;
A title that currently belongs to Galaxy 1 which sits at 12.76 million according to Nintendo:
https://www.nintendo.co.jp/ir/en/finance/software/wii.html

Splatoon 2 will be a huge seller, one of the Switch's best, but Odyssey will be on a class of its own.