Rumours of a Fallout: New Vegas 2 have sparked around the internet following an addition to Fallout 4's backend labelled "newvegas2."
While the branch has since been removed, that hasn't managed to stop the flood of speculation. In the past, we've heard about Obsidian Games' desire to return to Fallout: New Vegas, but considering the developer is busy with Avowed right now, we shouldn't expect a follow-up, remaster, or anything like that anytime soon.
Perhaps then, it could be to do with the next-gen update coming to Fallout 4, hinting that we could see some New Vegas content being added in with it. With over a decade likely to wait until Fallout 5, we're going to need some great extra content coming to Fallout 4 to keep us interested, so there is a chance the "newvegas2" branch is to do with that.