Though it still doesn't exist officially, God of War 4 is now available for pre-order at BT Games, a South African retailer. This is the same BT Games that leaked Mass Effect 3's multiplayer and the Jak and Daxter Collection's, so there's precedence for this being more than an ambitious placeholder. We've also confirmed that they operate based on information given by local distributors.
The site gives "Feb 2013" as the game's expected ship date, but that's a bit more nebulous in its reliability at this point. Still, add this listing with Sony Santa Monica's search for a Senior Staff Concept Artist and Timothy Williams' affirmation that he is indeed working on God of War 4's orchestral score, and we feel confident in saying -- yes -- there may be yet another game in a super popular franchise.