The Sony Japan Studio which has helped out on games such as Soul Sacrifice (developed by Marvelous AQL) and rain (developed by Acquire) is making a PS4 game.
News of the secret development comes from Famitsu Magazine [via], although fails to provide any further details. The same team is also contributing on Badman G, Destiny of Spirits (Q Entertainment), Over My Dead Body 2 (Alfa System), Freedom Wars and Soul Sacrifice Delta. So it sounds like it's keeping busy.
We're looking forward to seeing what the team comes up with.