Animal Crossing: New Horizons already is the best selling game ever in Japan, if you count Pokémon Yellow separately from Red/Green/Blue, at over 9.5 million and will end up over 11 million.
Splatoon 2 is still below 5 million.
There is no possible way in hell that Splatoon 3 sells over 10 million in Japan.
Yes, next year is very likely to be the Switch's peak in software sales in Japan, but ACNH launched at the perfect time and has been more popular before already. Both Wild World and New Leaf sold more than Splatoon 2.
Splatoon 3 would need to be a absolute masterpiece to sell more than 8 million unless it introduces some wild new ideas that raise the appeal even more.
I say 7 million is the ceiling.
Even Smash and Mario Kart won't have it easy to reach that mark.
Essay Pro