Coming from an interview with Gamingbolt.com Sega Japan have once again confirmed there are no current plans to bring over Yakuza Ishin.
Leonid: Will Yakuza Ishin ever get a western release considering the fact that it’s the #1 PlayStation 4 game in Japan?
Sega Japan: There are currently no plans at this time.
Aside from disappointing western audiences the interview actually has some really interesting details:
Leonid: Why did you decide to make Yakuza Ishin a spin-off, instead of the next main entry in the franchise?
Sega Japan: We had the idea of making a spin-off based on the Edo era from the start. In the previous Yakuza 5 game, we were able to put one break off to the modern time version and wanted to add more of an RPG type of gameplay in the next title. We felt the idea of the new game and the time setting of the Edo era matched and so Yakuza Ishin was created.
They also go into some great stuff about programming on PS3/PS4. Definitely worth a read if you want to get into some of the fine details of Yakuza Ishin.