2chan, the latest issue of Famitsu quotes Yakuza series director Toshihiro Nagoshi as stating that the game is a direct sequel to Yakuza 2, and is in development exclusively for PS3.
Nagoshi states in the Famistu article that Ryu ga Gotoku Kenzan! – which is set in Edo-era Japan – is actually considered a spin-off from the "main" Ryu ga Gotoku series (Yakuza here in the West). No release date has been announced for the series' third (well, technically fourth) installment, but we'll keep you posted.
[Via PS3 Fanboy]