I know they said they would probably not do it, but really..
Multiplayer.. Cooperative.. Campaign.
Come on, this would be an AMAZING idea, and it would be so much fun, unmatched by any game out there in my opinion. I honestly think that it would be hours and hours of endless fun.
On one hand, you have two people fighting together in a single army (One army alone or two armies supporting each other), conquering the world with the power of friendship and real human intelligence. For example, one man could be leading the Archers/Siege Equipment during a siege, whilst the other man could be leading the infantry in an assault on the walls. The possibilities are endless.
On the other hand, when the power of friendship fails, one could join a separate faction and the two could do battle against the other, in two separate armies, which would create all new kinds of fun. Imagine this, one man and his army crouching behind the walls of a castle while his ex-friend and adversary attack those walls with their siege equipment. Or perhaps a massive cavalry battle between the two. I honestly think the possibilities are, as forementioned, endless.
It would seriously be pretty damn cool.