I already know I'm gonna get flamed for this but I thought of, I think it is anyway, a neat idea for a way to implement multiplayer in the game, and that is an arena DLC where you and a group of other players are set onto a large arena floor where you work together to take on waves of enemies with maybe some bonus rounds every x amount of waves like MUDCRAB SWARM!!! All while earning money and items to bring back with your single player file.

/zip up flame-retardent suit

On a side note, I think I've seen some people say that the game engine itself doesn't allow for multiple players, so if it isn't possible it isn't possible, I won't lose any sleep over it, I just think it would be fun.

All multiplayer and coop discussion go in this thread:
http://www.gamesas.com/index.php?/topic/1162506-official-discussion-of-multiplayerco-op-in-skyrim/page__hl__multiplayer