1) Much as I would probably complain about this, add zone-specific currencies that you accumulate by doing stuff in said zone. Fates, leves, sidequests, killing monsters in long chains for the handful of people who really want that, and hunts. This currency could then be turned in for zone specific cosmetics. For example, ruby sea would let you get the confederacies outfit, a kurenai minion, and some sui-no-sato furniture.

2) Zone "dungeons". Basically a giant fate that spawns multiple boss fights and trash in-between. Something akin to that Uldah event for the last anniversary, but out in the overworld and triggered by doing fates. More cosmetics and orchestrions to be gotten from this.

3) Vendors for said stuff require defending on occasion, with gatherers getting materials for war machines that crafters then craft and people could use to fight off invaders and the like. Make better gear for the npc guards to wear, etc. Good source of scrip and tomes.

4) Eureka bunnies, but they have a chance of showing up after any fate.