I question whether we should even have cities with 30 million people. That's probably a problem too. People like to point to what appears to be lower c02 emissions, but that's not the only metric that matters. Metrics that I care about would be something like independent farmers per-capita, bikes per-capita, distance of travel for produce, etc.
> People like to point to what appears to be lower c02 emissions, but that's not the only metric that matters.
On that note, central business districts & skyscrapers aren't actually that great environmentally, although the city model as a whole is much better environmentally than their suburban counterparts.
And it's certainly possible to build a dense, urban city housing even millions of people without a massive central business district. I think, more than anything, the central business district is an artifact of how we organize ourselves economically (IE the economy is dominated by relatively few massive corporations). This is harder to change but certainly not impossible.
When people left the military they went to familiar environments. You "paid your dues" just like a private did. You stayed with the same company. Etc. But that's all changing. Historically that was not the case (well historically we didn't really have companies for that long, but you get the point). So I think we will revert to a more natural flow, which is more decentralization and fragmentation. I think this is inevitable, but I wish/hope/want to avoid the waste of resources in creating these things in the first place.
Even in Shanghai there's plenty of neighborhoods full of life at a human-appropriate scale. Just not at city center.