A recent rumour that Obsidian Entertainment are working on Fallout: New Vegas 2 unfortunately turned out to be just that, a rumour. There is no truth to it at all, according PR manager Mikey Dowling who spoke to Kotaku:
"We've said plenty of times that we'd love to work on a Fallout again if Bethesda wanted us to, we just aren't at this time. Right now we're very focused on the Fig campaign to make our first ever sequel in Pillars of Eternity II: Deadfire. Whenever a new Fallout comes around though, whoever is doing it, we all look forward to playing it!"