I think it would be awesome to have world FATES/Quests that involve the whole server across various zones that have multiple phases.

The question would be what the rewards would be, and I would think that by completing the world fate, all players would receive a buff, plus other various world benefits. Different world fates would offer different buff rewards.

Some ideas off the top of my head:
Reduced Rates
Increased Gil Find
Reduced Gear Ware
Increased EXP
Increased Gathering
Increased Crafting

Anyway, just a thought I would share.

Keep up the great work.