Ill be posting regular updates on twitter on the progress of the co-op game mode. I have already built an initial test scene, and so far so good. Basic stuff like player spawn, position synch and the basic servers set up is already working. My way of approaching this will be by simply taking each basic gameplay system one by one and modifiying/redoing it so that it supports multiplayer.
So.. follow me on twitter if you are interested! @cnorori95