Ishgard makes sense as a target but Ul'dah may as well be soon an action-able location, with all the political turmoil. While I don't want to have a broken city* forever I think it would be quite neat if they have the process of the political structure deteriorating, evil syndicate members fighting for power, and the people fighting back in a war for the new Ul'dah. It would make a good dungeon but I thought maybe they could open up Sil'dih as a temp area that gets cleared out and then having a magnificent magical underground city..
Dunno, those zombies may be hard to clear out but I like the idea of change over time and like even more the idea that sometimes things don't "upgrade" but actually fall apart and are not rebuilt*. Ishgard upgrading sounds likely but that's not exactly what I meant, lol. Edit: I really like the changes made to Mor Dhona and other areas, not to put those changes down - but growth is the first natural expectation, destruction without literal regrowth is less common and both together I think make an even more lively world feeling, but again I've loved seeing the game make changes to areas over time.
Anyway more on point, I liked Besieged I thought it was pretty fun - consequences were interesting, I imagine they could bring back hamlets with consequences too. If they could make a FC housing instance It could be interesting if they had critical/useful NPCs and functions to your town, attacked by jealous and looting beast tribes building strongholds nearby, and interested enemy FC spy and war activity into a besieged content (bonus for participating but you can decide not to be admitted into a roster of attack-able towns).
*May initially seem to be conflicting points, I mean that I don't want the Immortal Flames and the people of Ul'dah to have a broken city forever - if they move cities then that new city would not be broken would meet the point of not having a broken one, even if it was a different place. Not that I don't mind Ul'dah it's quite nice, but someone was terrible enough to not put an aetheryte shard in the market area for a market focused city so maybe we do need to rebuild... lol