With the power of next gen consoles and cloud, this is very much possible.
With the power of next generation consoles, PS4 and Xbox One, and the accessibility of cloud services, it would be very much possible that developers may push out entire worlds as add on or downloadable content on consoles. See the MMO’s for example. The developers keep the interest high by adding new worlds/universe which makes sure that gamers will come back for more exploration.
Although not officially announced but rumored to be in development, Fallout 4 may have additional worlds as DLC after the game releases. So how does a core location of Detroit sounds as a downloadable location? There could possibly be an Ann Arbor as the DLC may allow the player to roam away from the locations. There could also be a DLC set in Ohio or even Fallout New Orleans and have a story based on how Caesar expanded towards the east and took control of New Orleans.
The ideas are all up there. What kind of DLC are you expecting from Fallout 4? Sound off in the comments section below.