Japanese talent and fashion model Ayana Tsubaki is quite involved with Yakuza games, having lent her face to previous games of the franchise as Kazuma Kiryu's favorite masseuse, and working as a co-host for Producer Toshihiro Nagoshi's own Nico Nico show.Today she took to Twitter in order to tease the platform announcement for the upcoming spin-off Yakuza Ishin (Ryu Ga Gotoku Ishin):

The two tweets embedded above basically say that the game won't be on 3DS, but it'll be on a platform that "won't betray everyone's expectations". The first tweet also asks if the franchise owes much to Sony, while the second teases September the 9th as the date in which the platform for the title will be announced, which very conveniently happens to be the same day in which Sony Computer Entertainment Japan and Asia will host the press conference that is expected to oust the PlayStation 4's release date for the archipelago of the rising sun.

You're free to draw your own conclusions, but I'd say the hints point quite strongly in a very clear direction named PS4.