The Age of Arcanum produced a surprising number of floating cities. IIRC before EXU: Calamity began we knew of Aeor, Draconia, and Zemniaz, all three of which have been destroyed. Now we have Avalir, which itself originated from a heretofore unknown continent called Domunas (though this could possibly be an archaic name for Wildemount, perhaps, just as Tal'dorei is known in this time as Gwessar).
BTW, wasn't it mentioned that Aabria's character was hypothesizing about plane shifting the city already? Perhaps the party could possibly end up sending Avalir to another plane (or even another Material Plane world) hopefully with less disastrous consequences than Aeor.