I think for Fallout 4 instead of carrying on further with the life of post apocalyptic retro style Fallout, they should do a few spin offs. I think they should do them on the major factions in the game; such as the NCR, BoS, Enclave, Legion etc. Make the story so that you're a soldier in one of these armies and that way we can find out more about their past and their fate... That'd be awesome! For example both the BoS and Enclave have both had their power diminished over the years so an in depth back story and fate (Which you get to choose) in the new game would be amazing. There's probably been other threads like this but I just visited these forums for the first time today . So yeah in short; I believe they'd be very successful for the Fallout universe, as the game has so many ways to go with the story, so why not visit the factions in depth?