Why wouldn't it be a PS4 game? That's where they make their money on the franchise. PlayStation systems. Only two other scenarios: PSVita (unlikely), or PS3 (no). AFAIK, Yakuza is always profitable.
With all the talk about Japan moving to handhelds and the fact that Yakuza 5 only sold 0.59 units. You can bet that a Yakuza on a new platform will probably sell half of that and with them needing to invest more into the game if its a PS4 title, idk it just doesn't make sense to me.