Multiplayer is a definite no in my mind, it would require excessive balancing and we would end up with weekly down time, more then likely. I do thing that co-op dungeon could be interesting. Something such as Fable 2... that would be cool for showing the game off to a friend now and then, but I don't think it would used much. I think if anything they should release the game without it and then release a mod/dlc/expansion that has a random & repeatable dungeon in it that allows for two players to link up, but that is the extent. To simply put a small dabbling of it into the game.