Sega is bringing Yakuza 1 and Yakuza 2 in HD form to the Wii U. Although it looks like there's a bright future for the series on Nintendo hardware, it'll need to sell well before anything more becomes of it.
During an interview Yakuza Producer Toshihiro Nagoshi shared the following:
To be honest, we’re not aiming to see if the game will be a smash hit. Our real intention is that we want to see how people respond.
The existing [Wii U] users are different [from PlayStation owners], so isn’t it hard to say if it makes sense? It isn’t jumping ship to Nintendo hardware, Yakuza 1 & 2 are coming out on the Wii U, and this is what it is.
Wii U software hasn't sold particularly well and in-fact has one of the lowest attachment rates of recent years. Furthermore, Yakuza will have to find a way to spark interest from Nintendo's install base. The series' mature themes don't fit well on the platform, either. The similarly violent ZombiU has sold around 400k units, a disappointing number for a flagship release title that was marketed heavily.
Yakuza 4 is considered by many to be the best entry in the series. It'll take some convincing before Sega is willing to invest time into porting a couple more games over to the Wii U.