The Switch would need to sell well over 20 million lifetime in Japan like the 3DS which I see very achievable since it will be the only dedicated gaming handheld on the market there in the next year or so, but even then 5 million is outselling the best 3DS game in Japan Animal Crossing New Leaf which sold 4.5 million going by VGChartz numbers, so... right now as bold as I can go is it selling over 3 million in Japan but who knows, anything can happen.
AC hit 5mil+ it has the best digital sales for a nintendo game. It night be over 5.2 mil right now
Yeah was thinking digital sales weren't included in that. Anyways it is the Animal Crossing team that makes Splatoon after all so who knows?