In a new interview with Famitsu (transcribed by ryokutya), Ryu Ga Gotoku Studio director Masayohi Yokoyama revealed that the studio is planning on creating a new game that is separate from either the Yakuza and Judgment titles.
Yokoyama flat out said, "we're also working on unannounced titles outside of (Yakuza and Judgment)." You really cannot get more definitive...