I do think that destroying the NCR would be extremely derivative. The idea of "War never changes." is supposed to mean that while people always have a knack for killing each other, society can continue on. "War never changes, but people do." And while I have great respect for Avellone, just resetting the lore to zero with "Nukes again" is definitely not my idea of what he would call "Making the NCR more interesting."
I think we should just forget about California, really. Not in terms of like, the lore and stuff but of returning there for a full game. Unless it was like a remake or remaster of one of the old games. I mean, we've been there. We've done that. New Vegas certainly has a bit too much lean on the NCR due to them being the most powerful faction and the Legion content not being fully realized, but I think it was /about/ right. Maybe a little bit less presence, especially the farther from NCR land you go but I do think that they should be in other places.
I don't exactly want Todd Howard's crew to ever try and touch on the NCR unless they get some freelance writers who really know what they're doing at LEAST but on a more in-universe level it's almost unbelievable that with all the NCR's power that they don't have like an embassy in The Commonwealth or at least in the Brotherhood controlled D.C. mentioned in Fallout 4. Not a standing army like they had in Vegas, but just an embassy.
Objectively, there is a very strong case that can be made for destroying the NCR again. Mostly that they're repeating the same mistakes America (and the entire world, in many cases) have made and now they're facing the same issues such as corrupt bureaucracy, resource shortages, war, annexing a territory for its resources, ect. Personally, I want the NCR to survive because it turns the rest of the country into "The Frontier" which is about the best "wasteland" you can get out of Fallout 200 years later without asking yourself what the fuck is up with this entire destroyed area.
But either way it would be more interesting to see if the NCR can overcome the things that brought its predecessor down or if it's doomed to repeat the same mistakes all the way to the end. And because of this, I think there should be at least one New Vegas follow up to answer that. Aside from, you know... I just want one. Not all questions need answers, sure. But the NCR becoming so much like America before it certainly raises a question that I feel deserves an answer.