There was this one forever-alone type nerd fat kit who managed to make Oblivion multiplayer but it had some drawbacks such as fighting animations weren't working properly and I do not remember if quests worked. But still, you could see your friend in your game and that was an improvement. One day in the forums, (of that mod's site) one comodder called the kid a nerd in a friendly way but the kid was so offended he closed the website and god knows what he did afterwards.
Now for Skyrim, a coop mod, while possible and done to a certain degree before, is not feasible and probably will never get realized. Though an arena type of multiplayer mod where no savegames are required and you choose your equipment from an in-game menu or an in-game container and fight your human opponent, or take on some generated AI opponents is easier to pull off. And I also would donate money for that. But I'm sure a multiplayer mod will commence as soon as the CS is released. Like all those before, they will aim to fully implement coop storyline gameplay and fail in the end.
Multiplayer mods were being made for Morrowind as well. From my experience over the years, I think we have no choice but to wait for Bethesda to add multiplayer COOP. But I'm sure if Beth goes into multiplayer, then the whole gameplay and feel of the game would change. So I would just sit down and enjoy my singleplayer gameplay and play other Multiplayer games for COOP at the moment.
