Actually if you Play GTA IV. with niko bellic in a mission intro, there's a plane ticket that said "State San Andreas" so maybe niko bellic flies to SA? or maybe one of the main characters like paki, or whatever his name is came from SA?
and "Seagull" in SA singleplayer there is a mission in San Fierro where you have to save Mike Toreno, he is kidnapped by the drug dealers in a van and they take him to San Fierro's airport, there's one part where T-Bone says.
"hey mike says he can hear SEAGULLS!" and then CJ says "shyt it can be anywhere in this town!" then T-bone says again " head to Eastern baysin!" so maybe it's taking place in San Fierro also known as San Francisco,
maybe they will make SF SUPER BIG!! and it will take place there?
i have many conspiracies, too many to type down.