It'd be very hard in OP2.. Even though we can write missions from scratch, multiplayer programming is a little odd at times.
Reason being, multiplayer wasn't designed to be played that way (but I'm sure it could be done)
Question: Why coop missions? Unless you made a totally new "campaign", it'd be pointless to make the existing colonygames/campaigns into coop (because the AI is so bad, thats the programmer's faults -- the AI is implemented in the DLLs not OP2).
Btw: topic moved.