.....what should Sony Santa Monica work on next? Since God of War's story is end with the release of III, they will be free to work on new IP or visit an old one.
And to answer the people who will say that God of War isn't going to end. Sony has stopped franchise development on successful IP's in the past. Wild Arms, Arc the Lad, Dark Cloud (there hasn't been a new one yet), The Legend of Dragoon, Sypro (Sony stopped, Universal picked it up and ruined it), Crash Bandicoot (Again Sony stopped, Universal picked it up and ruined it), etc.