Instead of community milestones, why not have Summoner Raid Events?

Said Raid Events can be far more engaging in getting the whole player base to actively participate in whittling down the HP of a super-boss over time. Along the way certain milestones are unlocked, and once the boss has been defeated is where the true rewards are awarded.
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Or maybe the pre-raids would see the community team up to take down 4 of his heralds before we gain access to big purple hat.