According to the creator’s comments on the NexusMods page, the idea came about after visiting New Mexico in real life: “Santa Fe, ABQ, and just the desert was a delight! Then my brother had told me about Project Roswell and the Manhattan Project, and thus arose the idea of a Fallout mod in New Mexico.” To give you an idea of the scale and level of dedication in this thing, they’ve already uploaded trailers for this mod - very well-done trailers, too. The mod is called “Fallout Nuevo Mexico,” and it can be found on NexusMods, where it was uploaded by its creator, VerasTeam2077. It’s due to launch in full sometime soon, though the creators have not specified a release date or an exact story yet. In this case, a huge Fallout: New Vegas mod is looking good enough to almost be an actual sequel to the game in question.
Mods are always a fun way to add new life to a game, particularly one that is already several years past its launch date.