I keep my predictions conservative so I'll say not likely, though not ruling it out entirely. Splatoon is definitely a "four quadrant" type of game, the first was extremely well-received and there's little reason to doubt the sequel will be at least as good, probably better. It'll depend on exactly how hot the Switch still is throughout the holidays, I think. If it's really exploding like the Wii did in its second holiday then anything's possible, I guess.
~5 mil by the end of the year would also be close to 50% attach rate, unless Nintendo's estimates are exceeded.