For one thing I am sure, and I have a couple of theories for you:
First, I'm pretty sure GTA V will definalty not be in SA, because Rstar wont spend time on empty places.
It will only be in one city. As of next SA, it will probably be with different missions and characters, but same graphic, like other stories (LCS; VCS..) and in my opinion they would release it somewhere soon, while waiting for new Engine to make GTA 5...