They're not going to remaster Fallout 3 and/or New Vegas unless they intend to bring it to all platforms. At least, it would completely shock me if they did and it would shock a lot of fans who are waiting for a remaster of those games on PC, Playstation, and Xbox. There is no reason for them to piss off so many long-time supporters and there is no reason to leave so much money on the table by remastering those games for what would likely be its weakest market.
Beside that, the Gamebryo Engine was a mess even back then, it would be a nightmare to bring forward now. That's not a minor undertaking or something you easily hand off to another company. Bethesda would probably have to do that themselves, which would take them away from other tasks. Even if they have one of their new studios working on it with supervision from the core unit, it would still take a long time.