I'm not sure how feasible this would be for the developers' side but it would be cool to have co-op for all game modes (players vs AI bots).
That way you can learn how the game mode works without being completely manhandled by a 9 year old Korean kid.
Plus you would also be able to learn the different maps.
I don't see how any players could be opposed to this. However, the developers might not think it's worth spending time on. I'm thinking you have to "map out" all of the AI stuff in new maps and game modes but I have no idea how that stuff works, lol.