Honestly it's pretty hard to predict. I think 5 million is guaranteed just because of how strong the franchise is in Japan. Splatoon 2 and Splatoon 3 roughly did 7.5m and 5m respectfully outside Japan so because it's a spinoff I could see it do 3m/3.5m outside Japan, and then a little bit more in Japan.
So something like 7.5m/8m lifetime







