The lead developer on ambitious-looking Fallout: New Vegas mod Fallout: Nuevo Mexico has canceled the project in order to prioritize his "mental health" and to "face reality".
In a message shared on the mod's Discord server (via TheGamer), developer Zapshock says that while Nuevo Mexico has been his "passion" and "obsession" for years, the project's workload and costs are "too great".
As such, continuing with Nuevo Mexico's development "simply isn't sustainable for [Zapshock] and everyone involved, including voice actors", and so the decision was made to cancel the project. Zapshock says the decision was "painful", but "necessary".

Before its cancellation, Nuevo Mexico was set to be a mod roughly the size of one of the Fallout series' DLC packs, and it would have taken you to the US state of New Mexico, as the name suggests.
The mod was to be set five years after the events of the original Fallout, putting it several decades before the events of Fallout 2 and New Vegas, both of which take place as humanity is beginning to rebuild something resembling a coherent society.
Per a Game Rant interview from February last year, the modders were planning to include Dragon Age-style origins for characters in Nuevo Mexico, including one for a ghoul character, which would have fundamentally changed the mod's gameplay experience.
Honestly, it sounds to me like it's no wonder the mod was canceled; Zapshock and his team clearly had an insane level of ambition for Nuevo Mexico, and with just four people working on the project, they were bound to burn out sooner or later.
Nuevo Mexico isn't the only Fallout mod to have been canceled in recent months; back in October, the developers of Fallout: Vault 13, a mod that attempted to remake the entirety of the original Fallout in the fourth game, shut down their mod due to "a combination of factors".
If you are looking for a DLC-sized Fallout mod experience, however, all is not lost. There's still Fallout: London, which launched in July last year and which had attracted a million downloads by October. It's a Fallout 4 mod, though, so you'll need the base game to play.