There's no point in making Fallout 4, because Fallout is dead.
The decline in setting started with Fallout2, really, and the infection propagated into Fallout 3 and New Vegas.
Gone is the spirit of Fallout 1, where they watched Mad Max on a loop while making the game, and where Tim Cain wanted to explore the details of a post-nuclear world. It's gone. "Fallout" is now a series of boring quests with generic factions, occasionally littered with aliens, The Matrix, vampires, talking deathclaws, cowboy robot sheriffs, apparitions-by-any-other-name, talking trees, and all kinds of other inbred thought-deformities.
Its universe has become a 13-year-olds' first draft of a sci-fi novel, an "eclectic theme park", as opposed to a coherent setting. Its "walking simulator, shit inventory, shit combat" gameplay is endured, rather than enjoyed.
The post-apocalyptic RPG genre isn't dead. It would be great to see something inspired by say, "The Road". But the franchise known as "Fallout" ran off into a ditch a long time ago.