I can see it now, the main character will be...LB. LB was somewhat of an unknown character, yet seemed to be close friends with Ryder in GTA San Andreas. LB most likely had ties to the Orange Grove Families (OGF as you know, was made up of several affiliate gangs such as Grove Street, Temple Drive, Seville Boulevard etc. but had a falling out early in San Andreas' storyline). I expect him to be black, and probably knows nothing of CJ because we know the two never met in SA (LB may know Sweet and possibly Smoke, but we're uncertain). But he seemed to really know what he was doing, like delivering the robbery van and other honorable mentions during Ryder's missions.
It's a long shot, but hey.