I believe the feedback thread in question is here.
My favorite (and well, only) memory of these kind of events comes from EverQuest and EQoA years ago, where you'd get GMs or devs masquerading as monsters and rampaging through cities, inviting everyone to try to defeat them. Unfortunately this really only worked as a spontaneous thing, if you happened to be in the right place at the right time. As one of the devfolk mentioned last night, if you advertise such things in advance, everyone and their grandmother shows up and overloads the zone, killing performance or even crashing the server.
On the other side of the coin, you can't really have small cozy events for just a handful of people, as that leaves most everyone out.
I think the scavenger hunt idea is the most viable. The devs could hide in their houses and chat channels and give hints through server messages, and objectives could be spread through all the zones so everyone isn't crowding in one place, and characters of all levels could participate.
Bonus points if the broadcast messages are totally IC with a unifying theme — say, the devs all roleplay as Protostar workers asking everyone to recover goods from a shipment gone horribly, horribly wrong.
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