Adding online play for consoles via update is a great idea in my opinion. I've read complaints that it would become a competitive game, higher levels would troll lower levels, and things all surrounding the PvP aspect, which would still be really fun. But it's as simple as joining a PvP or non-PvP game, or creating a game with your own interaction preferences (such as friendly fire, pickpocketing players, and maybe even a max level setting). Upon starting a new game and completion of the tutorial quest, you could then pause the game and go to the "Online" tab and choose; open/private/friends only, PvP/non-PvP, max player level, or even not play online at all, and other options in order prevent players having a bad playing experience because of the others joining and ruining one's game. Say you get invited by a friend and you accept, once the game has loaded you could choose between your saves/characters as your loadout. The game has a lot of ground spells and things that could really be put to use in a group of adventurers searching through all the dungeons of Skyrim together. It would add an exciting aspect to the game that I think it could really use to attract more players and for players who have reached max level, or are bored of adventuring alone or with a relatively stupid NPC follower. As I said, these are merely opinions on how I think it could be extremely fun to add a system like this. Lemme know if I'm the only one on that.

A game has to be designed for co op at the beginning of development. It can not simply be added in an update.

Geez, no, what you really want is an MMO, and TESO is already on development. I like the game as it is, only single player.

We have a thread for discussing non-MMO multiplayer TES here: http://www.gamesas.com/topic/1366657-non-mmo-tes-multiplayerco-op-thread/