I know that a lot of people really don't care about having a game with co-op. But I would like to see the story line have the ability to join into someone's game and play along side with there friends. The AI can raise the difficulty and introduce more enemies for each individual person who joins into your game. No online pvp games, but an all out 4 person team against an ever increasing environment. Plus have the ability to have some exotic gear and weapon drops or treasure hunts. Just a thought.

Never. If you want to play co-op, play a game that has it. I'd rather Bethesda didn't waste time on feature like co-op.

When it's no longer a Bethesda game. (Also, a completely different engine, built from the ground up for multiplayer.)

...also, get your dirty multiplayer off my singleplayer games. There's few enough SP games as it is, what with MP being crammed into so much stuff where it's not needed/wanted.

You can discuss multiplayer ideas in Fallout here: http://www.gamesas.com/topic/1512524-fallout-multiplayer-discussion-thread/