I'm not sure about patches or updates but it sounds like the MMO style stuff is like a drop out/drop in system but it's not like Dead Island's. It sounds more natural, like the game decides whether to add someone to your game if you're doing the same quest or something. I dunno. That's what it sounded like in the GI article.
I think the reason why its multiplayer isn't clear has something to do with why it's there in the first place. To put it simply, this isn't an MMO. This isn't the kind of game where a lot of players participate in an activity to make it a different experience to a single player game. You have to be always online only so a few players could join your otherwise single player campaign. Online multiplayer could've simply been an option rather than forcing it down your throat. Sadly, we seem to have a case of a tacked on excuse for an always online DRM.