There should be an "Enemy Invasion" random roll in Destiny. Where you'd be playing in the crucible and then the announcer would come in and say to everyone "The enemy arrives. Work together guardians" and the team separation would disappear and everyone would have to try and stop the massive enemy incursion. It wouldn't happen all the time but once in a while and it would be epic
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I think it would be better if they did that with the social area instead, have a few fallen skiffs come in and attack the tower, afk guardians would be kicked to orbit and anyone active would pull out there gun and go to first person