But this is basicly "it" in my opinion. They could have just stuck with one storyline - the NCR victory, and leave the rest for future games/DLCs... but no... they sealed the fate of ALL the western part of the Wasteland, storyline-wise speaking, for further mods. Now imagine yourself: three endings. That even if they do make a followup - there will be a conflict, because each ending is just as valid and invalid at the same time! Now the ONLY solution is a PREQUEL!
Thank you Bethesda, I specifically paid fair and square for both your games in hopes that you now have destroyed.
Or... They could just decide what ending is canon and roll with it.
Player - "But I sided with [Insert faction]!"
Obsidian employee - "So?"
They don't need a Mass Effect thing.
They don't need a bunch of what if's storylines.
All they need to do for the next game is say that "NCR ending in canon".
So what if "I" sided with Legion?
If the main storyline for lore and canon reasons need to have NCR win then so be it.
So "the only solution" is not a prequel.
A sequel is very much possible.
A DLC on the other hand... Nope.