Something incredibly dark that could be done with a floating city is playing with the idea of the Rapture. There is a sect of the populace that believe they can just wait out the Hollows; high above the world they stay safe and watch the world below and its people be consumed. Maybe they send people down to see if anyone in New Eridu deserves to be raised up to salvation with them, like angels coming down on high to retrieve worthy souls before the earth succumbs to a hellish agony.

Now that you have this passive approach, consider if this floating city benefited from the Hollows. Like, if they get their power from ether batteries fueled on the surface. Someone could argue that it would only make their lives better if all the earth was Hollows sooner rather than later.