So I constantly see requests for Bethesda to remaster 3 and NV like they did for Special Edition which I would also love to see but I feel as though the community doesn't distinguish the difference between Skyrim and Skyrim SE compared to FO3 and NV.
First off, Skyrim was CREATED on the creation Engine and was simply ported to an updated creation engine. With FO3 and NV they were created on the Gamebryo Engine which handles scripting completely differently and porting a Gamebryo game to a Creation Engine would be extremely difficult/buggy if not impossible. Which leaves Bethesda with two options: Either tweak the Engine that is already around FO3 and New Vegas or rebuild them from the ground up in the Creation Engine which would be on-par with making an entirely new game.
Another huge issue with simply upgrading/porting the game to a newer engine would be that New Vegas/FO3 would still need completely rebuilt. New Vegas/FO3 also use different meshes/lower quality meshes that would need rebuilt/edited which would also be very time-consuming.
So for now the truth is, I think I'd rather use 4g patchers, graphics mods, NVSE plugins, etc because I ultimately think Bethesda would likely do some BS remaster to the game like patch the exe to support 4g, upgrade textures to 2k and maybe upgrade to a 64 bit system just to turn it around for $40-60.