Putting it at 4 million based on whether "Nintendo stocks enough" doesn't also warrant it selling 4 million in a year though?
It can have the most amazing line up of games in Japan. So did PS4 and Wii U, but that did not earn them 4 million units of hardware sold in a year. Especially today, where home console sales are at an all time low in Japan.
You are saying the Switch will single handely revive the entire console industry in Japan (which has been dead since Apple took over the world), because... it has a killer line up of games?
The hype is for the Switch is crazy, I know. But it would literally have to freeze hell or shake the entire console industry in Japan for it to sell 4 or 3 million.
Perchance you have never heard anything about the Switch? It is a home console that you can take with you. That bold text holds value that the PS4 and Wii U do not have. If you can take it with you it can sell 4million+ a year, if you can't it won't.