An interesting mechanic would be an item or a timed buff where you are boosted by light, (say by standing in a ray of light in the boss fight) which effectively is the other guardians who perished shining their light upon you, which is enough to boost you to a level where you can damage the boss. It could change locations so you are required to move to the light to kill the boss, not just sit in some safe spot and gally/ice breaker the boss to death. Imagine if Bungie took some of the ideas on this form and implemented them into strikes and raids. I've seen enough content on these forums to make a whole new game, let alone 2 raids per DLC.