NO I IN TEAM
Co-op in games usually comes in two flavours: firstly, there's the kind of co-op where you're going about your business when a second player drops in to your game and starts killing some bad guys with you. He hangs back and gets the kills while you push on and do all the important stuff. That's fine - there's nothing wrong with that, and it usually ends up being an enjoyable enough romp together with a friend.
Then there's the second kind, games like Portal 2 and Splinter Cell: Chaos Theory - co-op games that actually put the emphasis on co-operation and teamwork. These games leave players with a stronger feeling camaraderie and joint-accomplishment, the defining qualities of a good co-op experiences and what we want AC3 to focus on creating.
Perhaps in the co-op mode here, special abilities or equipment could be given to each character, forcing players to work together if they want to succeed. Double team assassinations and combat attacks could require strict timing, which means players will have to have excellent communication skills. There could even be certain enemy types that can only be defeated by using different co-operative tactics or double-team moves, and maybe platforming sections that require players to work together and trust each other to advance.
It didn't need it, but we think Arkham City did miss a good opportunity for some Batman and Robin co-op, so maybe Assassin's Creed 3 can help fill in that gap. There's definitely room in the market for co-operative Assassin action.