Alright, I know this will never catch on. Fallout 4 will likely take place in a very different place, with a very different plot, but hear me out. I think Fallout 4 should take place in the Boston Commonwealth, mentioned in in Fallout 3(the best game ever). The plot would be that after their defeat in Fallout 3(the best game ever), the Enclave retreats up to the Boston Commonwealth. Because of their lack of resources, and reinforcments, they are forced to join the populace of the commonwealth.
The actual game takes place ten years after the events of Fallout 3(the best game ever). Now completely convinced that the Capital Wasteland Brotherhood of Steel will not go back to the old ways, the Brotherhood Outcasts leave the Capital Wasteland. They stummble across the commonwealth, and in the process, the Enclave. They come to two conclusions. One is that the Enclave are probobly still very weak after their crushing defeat from the Brotherhood. The second is that they are likly in possession of very powerful technology. So they go to war.
Your character starts out as a member of the Enclave, but can later switch sides. You would basically diside the course of the war, and the victor. One last important piece of information. Because the Enclave have been with the people of the commonwealth for ten years, and the Outcasts are the invaders this time, the Enclave would be the "good guys" of this game.