I dunno hey. While I was playing the game the other day I started thinking about how coop would work in the game and all I saw were more troubles than it would be worth. Your co-op partner could really mess up the game for you and completely ruin the experience.
Killing NPC's, stealing etc. Plus the sheer complexity of the game just wont lend itself to a solid co-op experience. Bethesda would have to be mad if they ever considered going that route.