It's on open world game and it would be diffcult to make a multi-player. it would also take too long to find the other players
while it would be really fun, no one would get anything done and everyone would be just killing each other.
I think it could definitely be done. If they were to use the same kind of method as the Red Dead Redemption's multiplayer which allows a decent number of players to interact or mind their business on the same map.
There would be a major problem with the whole VATS system with multiplayer.
How epic is your character? Epic enough to slaughter armies? Now put a bunch of those demi-gods in a small space. Compensating for this would remove the Fallout element from the game.
It'd be difficult, but not impossible. The thing is, you're either gonna have a bunch of PvP demi-gods, as others have stated, or you'll end up with "sit around and do nothing in a wasteland settlement", and that wouldn't be fun, huh?
Red Dead Redemption had a similar issue to VATS with Dead Eye, but they found a way around it.
Ah, red dead. I love exploring with friends, and then getting surrounded by assholes with snipers, spawn killed for half an hour, and then selling the game (Brand new, only 1 week old!) for $15. Thats how much that horrible gameplay was worth to me.
Well, I got alot more out of my copy of RDR. Plus, its multiplayer was on the side where as I think a Fallout multiplayer would of course have to be the entire games core.