I think everyone in Japan has a PS4 already.
I think it's better to say that most people that want one, have one. Platstation just isn't as dominant and popular in Japan as it used to be.
Playstation 2 sold over 23 million units
Playstation 3 sold 10.5 million units
The potential is there but Japan has transformed into Nintendoland throughout the years, nothing to do about it really.