Cosmic Exploration and Ishgard Restoration were amazing events!
I was scrolling my screenshots today, one in special made me emotional: we had just unlocked a new region in Phaena, everyone was running together to the new spot for the next expansion event!

So, my proposal is that the combat equivalent, the Exploration Zones, could start like that, through the community effort the base gets new buildings and functionalities, new areas become accessable and with expansion events!

The expansion events could have stuff like the adventurers fighting hordes of monsters, defending our base, bosses appearing out of nowhere.
Also, make these events replayable after its completion.