Not very.
Kirkbride, a former Bethesda dev who worked on Morrowind, said ages ago that Bethesda always has the next two games or so planned out. Which is why you can find hints to stuff that will happen later, such as the destruction of Morrowind post-Oblivion/Pre-Skyrim, as far back as Morrowind.
Bethesda has a number of NPCs in Fallout 3 repeatedly mention D.C., The Pitt, The Broken Banks, the Commonwealth, and Ronto as the big cities/wastelands of the east coast.
We got D.C. in Fo3, and The Pitt in the DLC of the same name, it was only logical we would get The commonwealth, Ronto, or The Broken Banks as the next game setting, and given that more people mentioned The Commonwealth then Ronto or The Broken Banks, it was top of the list for Fo4's locations for anyone who knew BEthesda's habits and patterns.