Sounds good, ive gone back to the first one, i never did complete it.
I doubt it would be out for ages tho. The multiplayer idea sounds good, Maybe Co-op aswell. I never understand why people complain how multiplayer ruins the game when they are not forced to play the multiplayer at all, it has nothing to do with the single player. And rockstar are pretty good at adding multiplayer and making it as good as the single player without taking too much attention away from the single player, but making the Multiplayer entertaining and not just somthing you play for 3 matches then never go back to.
A new school, character, and area would be good, Maybe even creating your own character...