Okay, so one of your creative types need to make a co-op mission and post it for us all to enjoy. Don't go hogwild and decide to make a co-op CAMPAIGN... just one mission.
Here are some of my ideas:
1. Make the setup SIMPLE.
a) The team gets X number deployment points to spend and they decide who controls what figures. By doing it this way you probably get a better lock on the difficulty level in playtesting.
b) Use an already existing map in the core game. If you do, more people will be able to access it and setup will be much, much easier. Also, it will allow you - the creative person - to focus on what we - the players - care about most: gameplay.
2) Make the events STREAMLESS but UNEXPECTED.
a) For example, there could be a sheet of "if this then see page".
AFTER A REBEL OPENS THE FIRST DOOR: Page 2.
AFTER A REBEL OPENS THE SECOND DOOR: Page 3.
AT THE BEGINING OF ROUND 3: Page 4.
IF NO DOOR HAS BEEN OPENED BY THE END OF ROUND 2: Page 5.
Those pages will lead somewhere else, kinda like a choose your own adventure book.
b) For the unexpected events (not random), a player rolls dice. For example:
Page 2:
"After battling your way past the guards and blowing down the blast doors you are frustrated to see, though not surprised, an e-web and imperial officer guarding the terminal."
Roll a yellow die, if 2 surges the e-web is elite. Roll another yellow die, if 2 surges then the officer is elite. Roll a red die, if you roll a surge include an elite stormtrooper group.
3) Make the AI SIMPLE.
a) Enemy brawlers and guardians always pursue the nearest enemy.
b) Enemy hunters always pursue the weakest unit they are able to reach after having moved their full number of spaces.
These are just ideas. I'm sure you guys can do better!