My enjoyment from playing these games comes from being awestruck and being immersed in the world around me without even really noticing or making an effort to. It's not actively roleplaying really, I don't come up with a backstory for my character or whatever and I have never done that with any RPG I've played.
I think the Elder Scrolls are in a really unique position in this regard. All the seemingly useless features, like being able to pick up and throw calipers or following and observing an NPC during their day have really help add to the immersion. I think the crowd Oblivion attracted is underestimated a lot on these forums. I think Oblivion did the same thing for them, it made casual gamers realize how amazing a game is when it really pulls you into its world. It's a little embarrassing, I'll admit but I think it's true.
I really think having a Multiplayer or Co-op option would ruin that. I think the games should continue to make people fall in love with the Elder Scroll's unique brand of entertainment than try to emulate what other games do.
I agree on everything you said except the part about the multiplayer, it really didnt have to be anything else except a standalone feature, the only way it'd "damage" the game imo would be because it would take time from the dev team that could otherwise go into the singleplayer part of the game. Otherwise it wouldnt, just like if someone would mod a playable "multiplayer" experience of anykind to Skyrim.
And that's the only thing we can hope for, we already know that Skyrim wont have any sort of in game player to player interaction, but maybe this new game engine will allow for it being a "modded" feature, who knows what built in resources the creation kit will have, maybe if we are lucky Bethesda will do like Rockstar that made the GTA games more and more prepared for multiplayer until the consumers themselves had made a working base for multiplayer gameplay so rockstar could see that it worked and didnt risk anything until they could just include it in their next game, ha ha, pretty much like Beth is already doing, but with singleplayer mods, how much stuff modded for morrowind didnt turn up in oblivion? and the same thing with fallout 3 and new vegas, I'm sure we'll see stuff and features from oblivion mods now included in vanilla Skyrim.