How about if Blizzard makes a Co-op map where players spawn separately from each other?
One player spawns in the top left corner and the other in the bottom right, for example.
This forces both players to fight their way through the enemy lines until they either reach each other or the centre of the map, where the primary objective is. Once both players reach the centre of the map, they have to defend it for a short time ( 5-10 minutes ? ) from BIG waves of hybrids.
It is kind of like a maze where you fight your way out.
Air units cannot fly through the maze, there are also limitations such as impassable terrain (like tall mountains and buildings).
I think separating both players, fighting in different locations at the same time and reuniting at the end gives another vibe to co-op.
What do you think?