Not now
Not ever
My opinion is that any sort of multiplayer or co-op would severely diminish the single player experience. TES is a role-playing game, therefore, gameplay is more than combat, it is about open world exploration, dialogue with NPC's, and story (in the which you, as the player are the main character). Adding any form of multiplayer/co-op would completely change every aspect of the game and not for the better.
Multiplayer is on the rise as a gameplay feature, but it would be a shame to lose one of the few great single player RPG's.


