Yakuza 5 has been confirmed as in development, so says Famitsu magazine! It is the sequel to Yakuza 4.
This was revealed by Yakuza series creator Toshihiro Nagoshi himself who has recently formed a studio dedicated to the Yakuza series, aptly called “Yakuza Studio”.
There are reportedly no less than two Yakuza games in development.
Not only Yakuza 5, but also a PSP sequel to the previous PSP spin-off Yakuza Black Panther with Yakuza: Black Panther 2. It will retain the basic gameplay systems of the previous game and is scheduled for release in Spring 2012.
Here is a trailer for Yakuza 4.