A dedicated Fallout: New Vegas fan is making a mod to turn Obsidian's beloved open-world action-RPG into a multiplayer game.
To account for the influx of players, the mod will disable VATS completely. Going into your inventory will freeze your character into place and make them impervious to damage until they return to the game.
The mod also won't support New Vegas' DLC, nor will there be an option for private matches, though this feature may be added in time.
Mr. Mouse explained that quest lines will be synced, though the solution sounds inelegant at this juncture. "The way it works currently is that quests are clientside, they still take place in the world but one player in a location will synchronise entities/NPCs to other players around them," the modder explained. "This means that if you entered an area where a quest NPC should be, and someone has previously killed them in the cell (whilst someone is currently in it with you), then you will fail the quest on entry."
Here's some early test footage of the New Vegas multiplayer mod in action: