There's nothing new about that trend There have been single-player RPGs with a coop option since the mid-nineties. Just not something gamesas ever chose to do with the TES series, primarily for narrative reasons: they were going for the "sole hero saves the world" idea, and ANY kind of multiplayer including drop-in coop has to be taken into account in the story.

Doesn't mean they won't do that in the future though. Might be OK, would depend on how it was implemented I guess I'm not opposed in principle. With coop RPGs, you get the whole issue of how to connect people -- whether the publisher just provides a matchmaking service or actually designs the game to run on its servers, and then how you deal with mods, griefing, pvp etc etc. For every game that goes this route there is a lot of contention about exactly how to implement it, and no matter HOW it's implemented in the end, there's at least some ongoing cost for the publisher in terms of getting peope together (unless the multiplayer is literally LAN-only, haven't seen THAT in over a decade I don't think )

So it's not a trivial thing to add to any game, although people seem to think it is

But as the others in this thread have said, that's a completely separate issue from ESO. ESO is the MMO Elder Scrolls game, not the small group coop Elder Scrolls game. Different tech, different design considerations, different economic considerations, only partially overlapping audience. Neither one of those rules the other one out.

Watch Dogs already has that covered. The MP feature is automatically disabled during main/side missions. So it won't affect the story in any way. But it still allows you to interact with other people.

Obviously this is not the only way of implementing this feature. The other games I've mentioned utilize it in a way that it has more of an affect on the game world and the story.

I was thinking the same thing in reference to a Borderlands jump in and out kind of system but my one hold up there would be the storyline. I think we can all agree that Borderlands wasn't story centric. Elder Scrolls storyline, whether main quest or even side quests, change the world like Fallout. If players were jumping in and out randomly and missing things, they would really feel like they missed out on a big part of the game. I think that is what makes 4 player MP difficult for the series.