Some serious people are envisioning - and planning - floating cities
I see nothing about this idea that would make it impossible. There are lots of resource and waste issues to contend with, but we have the knowledge and creativity to solve those, I'm sure. And as with space exploration, I think there will be beneficial by-products in the form of real-life experience of managing a closed system - which we're not very good at, right now. Maybe some of the benefits would be in learning how to neutralize selfish assholes who would subvert communal survival for their own greedy gains. Just sayin'.