You know what I'd want?
Hawaii. All of it. Not at first, obviously, that'd be far too tremendous, but at least the main island, and make the others DLC. The main story would be the discovery that the volcanos are about to blow their load and you're a young tribal boy/girl (the tribes being the only peoples to survive the war, being far enough away from heavily-populated centers and the vaults being covered with the volcanic eruptions initially following the bombs) who encounters several BoS scientists studying the effects of the war on submarine life, but were washed on shore after a vicious storm, and are desperately trying to help make an old battleship or aircraft carrier or something operational again so as to retreat to the mainland. Super-mutants, raiders, and the Enclave would be replaced by rival, sometimes ghoulish tribes attempting to steal the tech from your new comrades, as well as the crew of a military submarine that washes on shore about halfway through the main story who wants the ship in order to expand "The Armada", which consists of remnants from eastern-asian countries and their navies, pushed out of their homelands by the Chinese prior to the Alaskan invasion. After the main story is complete, a DLC would have you as what is essentially a pirate, landing on the west coast periodically to take supplies, or as you helping the scientists and landing on the coast permanently, being stationed at the BoS port, to make sure any of said pirates don't get their hands on the boats.
Bam, no Enclave, only the faintest hint of the BoS, and an opportunity to get a totally new perspective on the war and it's aftermath.
