Bethesda made a conscious decision to have Fallout 3 take place on the East Coast, as opposed to the West. Personally, I found the hints of the Commonwealth to be particularly telling, and my guess is that Fallout 4 will likely take place on the East Coast as well. Just how much influence is something going on, on the other side of the country (in a post-apocalyptic world where walking two miles is pretty dangerous, much less all the way to another coast) going to be expected to have on that narrative?
For myself, I'd rather future games be more vague than otherwise about the potential endings of the previous games (the idea of my own "official" playthrough being ret-conned after the fact by a newer game doesn't sit as an ideal situation with me.) Technically, that would make any of the endings (and most of the events within the game) "less" canon - at least if we're going by the definitions I've strongly suggested in other threads. But I think that's a good thing, in an ostensibly open-world RPG where personal choice is supposed to be a major element.
If Bethesda decides to ignore anything that happens in New Vegas, when it comes to making their own games, I doubt it's going to be because they feel Obsidian's contributions to be "lesser" than theirs.