Obviously they can't destroy a whole city, but considering how much of Ul'dah's current political landscape is discussed in optional quests around the city state... It comes down to three choices:
1) Encourage an understanding of the place individual quests have in the world's chronology
2) Propagate every change across every single quest that ever mentions anything related to it, consuming a ton of resources that could be better spent on new content
3) Risk nothing, change nothing
What I'd like to see happen is for all 2.0-2.5 quests be flagged in some way as "Seventh Umbral/Astral Era" timeline quests, while 3.0-3.X quests will be "Expansion" timeline quests. Kind of like how clearing the Praetorium unlocks a bunch of new quests that can only happen after the Main Scenario, new players going through for the first time won't know a thing about what comes next until they get there, and won't need to. They can do whatever they want to on their road to completing the main story without getting spoiled on things that come next.
And once they get to the turning point and the expansion, the other shoe drops. Quests they still haven't completed will, of course, still exist, but rather than propagate every single little change to the perpetual setting back across every single little quest, the understanding will be that these quests are, chronologically, episodes from "last season." Since FFXIV's world hasn't really moved forward much since the Praetorium, I understand this is an extremely difficult concept for many people to visualize, but I assure you I'm not talking about anything that will destroy the integrity of the setting with regards to other players. Rather, it's a way for every player to move through the timeline at their own pace without the need for an eternal status quo.
