You know....
PEOPLE CAN PLEASE STOP CRYING ABOUT THIS?!
I mean, some people have valid opinions, but some people really, really, are just being a little bit stupid.
First, the idea of it's there, so therefore I must play it!
No. If it was there, no one is forcing you to play it. No one. You can still explore on your own, doing whatever the hell you want, AWAY from co-op.
Second, the idea of Raaan0mn00b65 and dragons7ay3r joining your game and ruining it.
Again, No. In every game I have ever know, there are simple ways to stop people joining your game if you don't want them to.
1. Private Server = Just you and whoever you want!
2. Password = Just you and whoever you want!
3. LAN = Just you and whoever you want!
4. Kick/Boot = Just you and whoever you want, and you can boot the people you don't want!
5. The Mighty Ban Hammer = Just you and whoever you want, and you only have to kick people once!
Listen, my point is, I know a lot of you have very valid opinions, but please, other people, you know you don't have to have random people connected and you don't HAVE to play co-op.
I like the idea of co-op. Hell, I'd love the idea of an server style setup, with up to one hundred players! (It worked for ArmA) Just think, you and your crew set up shop in a nice fort, building your own armor and weapons, taking turns to patrol and keep a watch, when some bandits (other players) come and lay siege to your fort. Then a group of friendly soldiers might come along and have an epic battle worthy of song at the gates of the castle!
But, that is my opinion, and not relevant to this topic. Why?
Because, at the very, very, very start, the OP said "THIS IS DISCUSSING IF IT IS POSSIBLE, NOT IF YOU LIKE IT OR NOT"
I think we are getting off track.
Anyway:
OT:
It is possible. It would be better if Beth coded it in, but some modders back in Oblivion did it. Hell, I even used it. It was good, but you couldn't enter houses yet because he hadn't coded it in. Guess what his last post related to the houses was?
"BRB, getting sandwich"
And he never came back.
Sad. But, with Skyrim, the new engine and the updated, well, everything, it should be easier.
That's just my two cents.