SEPERATE CO-OP CAMPAIGN
As we said before, we can't see Assassin's Creed being linear, so co-op should definitely utilise the whole game world, but allow us to invite a buddy to jump in to our game. The co-op world should be a separate entity from the single-player campaign world, but rather than having a few shallow side activities, there should be a whole campaign there built from the ground up with co-op in mind.
We don't expect it to be as long as the single-player campaign - that would be a bit too ambitious - but we do want a decent chunk of co-op gameplay. We want want it to actually be a meaningful, ideally somehow fitting in to the Assassin's Creed lore nicely. Obviously at this point in time we don't have any details about the story and events in the game, but we think if the co-op campaign was set before or after the events of the single-player campaign, Ubisoft could weave the co-op story with the single-player story, and use it to flesh out some extra details or plot points.
We feel this approach to co-op would not only offer co-op gamers plenty to sink their teeth in to, but retain the strong single-player focus for the gamers who prefer to work alone, but offer a deep and engaging multiplayer experience as well.