I think it would be cool if Hive tried to invade and everyone inside the tower gets there point of view changed to 1st Person and has too defend the tower. They can have this as a random event, would be fun to have at the tower. Bungie can even announce when it is going to happen, and that it is a one time event.
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I don't care if they kill everyone as long as they take down the -blam!-ing cryptarch too