I think the Saudis mirrored "Wall" in the desert has aspects of arcology. But of course it's not a sealed environment. It is ambitious, and supposed to be self sustaining but I guess time will tell about that. Hopefully we'll learn from that and not make the same mistakes. But as you said it's the things that we don't know about or could ever imagine will be the real problems. Who's job is it to think of that stuff?