If no one is supposed to do it, why bother making it in the first place? That's about as useful as Daggerfall's map, which was the size of Great Britain or w/e. There's no point in making a massive procedural world, when 99.99% of people are just going to skip it via fast travel.
They could fairly easily make a map with tons of randomly generated stuff, stretching from Boston, to Ronto, to The Pitt, to D.C., and all the way down south to The Broken Banks, but why bother? You would just strip each of the places that actually mattered of tons of details and world building, since all of that would be spent in dev time making the procedural world content, which only lessens the quality of each importance place, reuding what we learn about those places to the small snippits of culture and backsotry we got on Fallout 1/2/Tactics' locations.
Its literally a system of quantity > quality. Which I would hope we would have moved past already.
And even Fallout 1/2 didn't make you actually go through all that empty nothing, and let you quickly bypass the walk via a highly abstracted map travel system. I would hope that if Bethesda went to such a large covering area system, they would stick to the format the older games used, since it was done for many still valid reasons.
I really don't see any reason to do it, besides to cover more important locations in one game. But even then, those other locations would be far better off as their own games, or DLC for other games, where they can receive far greater detail and development then if they were all jammed into one game.