There's a lot of bad blood between Bethesda and Obsidian. Bethesda royally screwed over Obsidian financially for Fallout New Vegas. Bethesda also doesn't like everyone saying that Obsidian did Fallout better (even though they did).
Bethesda has moved away from true RPGs like Fallout. Fallout 1 was a PC based RPG. Fallout 2 was a PC based RPG. Fallout 3 was a PC based RPG with a console port. Fallout New Vegas was a PC based RPG with a console port. Fallout 4 was a console shooter with a PC port. See the difference? Bethesda is targeting the casual gamer market now, not the RPG market. It might make them more money, or it might not. I don't know. Casual gamers don't dive deep into the game lore and obsess over the game for years. They play the game, then move on to another game. The long and short of it is that Fallout the RPG no longer exists, and Bethesda has traded their dedicated long-term fan base in for quick cash from casual players who have no loyalty to the game.
Fallout 76 is troubling for a lot of reasons, and not just that it's a crappy game. It shows that Bethesda is focused only on dollars. Bethesda is VERY FIRMLY on the creation club and microtransaction path. I guarantee you that Fallout 5 will be rushed through development (because they are focused on money instead of making a good game), will be a crappy game full of microtransaction crap (because they are focused on money instead of making a good game), and will have over-priced and underwhelming DLC (because they are focued on money instead of making a good game).
And it's not just Fallout 5. The Elder Scrolls series has been going down the same path. Morrowind had tons of interesting side quests and depth. Oblivion had many interesting side quests and some depth, but not as much as Morrowind. And Skyrim was pathetic. The main quest was fine, if you're into the same old tired trope of playing the hero that rises from nothing and saves the world (yawn). But the side quests were all underdeveloped and short. Compare the College of Winterhold quests to the Mages Guild quests in Oblivion. Winterhold is like ok, do a couple of minor things, and poof, you're the arch-mage. Wait, what? Shouldn't I have to do a bit more to take over the entire college? And Bethesda has milked Skyrim for everything that they can get out of it. They are clearly still so focused on money that they can't see anything else.
Bethesda's focus is in the wrong place. If you make a truly good game, you will make money. If you focus on making money instead of making a good game, you'll make some money, but players don't want to pay for crap. Ironically, by focusing on money, in the long term you'll devalue your franchise and make less money.
I have no hope at all for Bethesda games at this point. They used to rule the RPG market. Now they don't even make proper RPGs. I can only hope that someone like Obsidian steps up and fills the hole from Bethesda leaving their own market. It's a pretty big hole. There's plenty of money to be made there, and Bethesda either can't or won't make a game to fill that hole.
The sad reality with Bethesda in their current MONEY MONEY MONEY MONEY MONEY focused state is that the only way a Fallout New Vegas remaster would happen is if they thought they could make a lot of money with it, which means a focus on creation club and microtransactions. In other words, it would be a complete crap game. And there might be some legal complications due to their contracts and agreements with Obsidian for the original FNV. I don't see a remastered Fallout New Vegas ever happening. Too many legal issues and too much bad blood between the two companies.
A Fallout 3 remaster might happen, but it would probably require something like what happened with Skyrim SE. Bethesda was developing their new game engine (technically more of a major overhaul to their existing engine) for Fallout 4, and they were using Skyrim as a test bed for it. Then they realized that with a bit more work they could release a newer and better Skyrim running on the new game engine. Bethesda is supposedly working on a new game engine, so if they create new Fallout 3 assets and use that as a testing bed then we might get a Fallout 3 remaster. But I guarantee you it will be another crap game focused on creation club and microtransactions, because that unfortunately is the modern Bethesda.
I used to buy any Bethesda game that came out, because I just knew it would be good. Those days are long gone. I deeply regret buying Fallout 4 and the DLC, and I completely skipped Fallout 76. And I am definitely not buying the next Elder Scrolls game or anything else by Bethesda at launch. I've learned my lesson.