You have small cities dying all over the country side because it becomes difficult to justify paying for general amenities like hospital, schools, ... and cities where you quickly hit the limit of high density too. You can replace a suburban sprawl by high density block of flat, but you need to upgrade the infrastructure to support it massively and the cost does not scale linearly past a point.

Seems to me there is a sweet spot there in the middle where the cost of public infrastructure is effective, a variety of living style at various price points, and there is still enough people for modern service to be cost effective. A bit like Europe if you get rid of the top 3-4 largest cities in each country.

If there is something that is prime for disruption, here you have it: this is a problem everywhere in the world, this is a problem that is solved the old non technological way, but with an already proven way to solve the problem using technology. The only bit that is missing is the proper incentive and a well balanced set of already existing technologies thrown in to make up for the major incentive of moving in a large city: the jobs are all packed in there too.