I would love to see one that would take every guardian on a given planet to be accomplished and would make use of a vast area of that planet. Something like taking down a huge enemy mothership that is flying across the map. Players would have to get rid of the drop ship enemies and then hit the mothership with all they have until it's down. This event could happen once or twice a day with an alarm sounding on the tower to let every guardian there know where their next stop should be.