I was thinking a similar thing earlier. Put a fireteam together, pick a mission, and play as the enemy Boss/ultras/majors. Extra points if we have the ability to position enemy mobs, trigger adds, and define simple AI pathing. Let us save our mission setups on the servers, let people vote on which ones are best, let other fireteams play against us and vote to see who has the most creative approach to bringing forth the Darkness. Bungie wants to see "emergent player behavior"...they'll need to open up both sides of the fight to see the interesting stuff we come up with.