FFXV

Pokemon X/Y or some Youkai Watch game.

Maybe even Animal Crossing

I think it's worth pointing out that out of all the games on this list, Animal Crossing: NL has the best legs by far. Whether they'll be enough to put it ahead of X/Y lifetime, I don't know, but I'm pretty impressed either way.

If FF15 hit 2 million in Japan that would be phenomenal.  I feel only an exclusive monster hunter could go over 3million on the ps4 in Japan only. 

Main Final Fantasy games tend to sell more than 1.5 million in Japan on it's first week. Seeing as how FFXV has been very awaited in Japan, selling more than 1.5 million would be very easy. That said, even if it does end up selling 1.5m+ it'll probably only sell up to 1.8- near 2m lifetime or if the game ends up really good and successful a bit upwards 2 million - 2.5 million.

That said it's either Pokemon or Monster Hunter.

that nintendomination right there

I can tell you what system it will be on.

FFXV can certainly make into the list. But on which can top the no. 1 I thought the Yokai craze would but it would be either a Pokemon game, MH or Animal Crossing to be on top. I can't see any Mario IP or other franchise to top that Japan chart

Pokemon XY or AC:NL
Home consoles however I will make the predicition of Dragon Quest XI

Not really. I mean Nintendo have the big franchises on handheld to sell units drawing in any 3rd parties who realise that the industry can no longer really support 2 handhelds successfully, hell we are struggling to have 1 sell well. And the PS4 has been out for a year selling western games to the Japanese. I would be more surprised if Nintendo couldnt hold every spot this early into PS4's life.