One thing i noticed yesterday while playing it with a friend.
Sometimes there two or more NPCs close to eachother, you can sneak up on both of them, but killing one alerts the other.
So we had the idea, that we split up, sneak up on both, and when in position we count to 3 to Assassinate both at the same time.
Well...so much for the theory. It doesnt work.
As soon as one player kills his target, the other one cant activate it, because the other NPC is alerted.
So i think it would be VERY interesting if there would be a coop-system.
When in a party and both (or more) players can assassinate a target, acivating the Blade pops up a synergy window, where the players can confirm the action.
Everyone who does that then performs a synchronized kill on their target.