Well, the Multiplicity crew were doing this for a while, but then they stopped working on it and went over to mod HL2... It's really a shame, some of the ideas were really sweet.
Oh, and if there are islands for gangs, I think I should get my own personal island, since my ego is just that big. I need a pool, and 5 choppers, and some hotring racers, and all the guns, and a mansion.