Famitsu announced a new game from Inafune-san called Yaiba. Early magazine leaks say it’s a "new zombie game" for an unannounced platform(s). We should be getting more information soon since this sounds like Inafune’s surprise. Keiji Inafune also worked on the Dead Rising series and Dead Rising 2 started with "A Keiji Inafune game."
Update: Famitsu has a little more information about Yaiba. The magazine outlines four concepts: zombie, action, ninja, and mecha. Inafune says there will be elements in Yaiba never before seen in a zombie game. Comcept will reveal Yaiba via a video on September 13.