While I still think it's unlikely we'll get any significant content, this quote keeps popping into my head.
Jason Bergman when asked about Fallout 4 several months ago:
Not much is known about the setting of Fallout 4 so far. When asked to give hints as to the setting of the next Fallout game, Jason Bergman said (translated from Norwegian), "You'll get no tips from me. But the Mojave Wasteland was a fun place to explore, wasn't it?"
So, I guess possibly an expansion.