A diminishing supply of resources to manufacture with, as well as increased competition for everything from steel, to zinc, to water to electricity is what major cities face in the future. Some, like Detroit for example, face losing their manufacturing base to outsourcing, and then fall into a state of urban decay and shrinking population.
Many of the ones that are now industrial will not be industrial anymore. This is already happening in rich countries like the US. Manufacturing will move to lower-wage areas of countries and to lower-wage countries.
The response of Pohnpei above is rather strong one. Most certainly highly industrialized countries and highly industrialized cities face the problem of wages, and this enables other countries and cities with lower wages to become more competitive. But the shift of industries from one region to another on account of low wages can only be marginal. It can never be substantial.
Regions with high wages have high wages because of higher standards of living made possible by high degree of industrialization. If substantial part of industries shift out of a country the country will no longer be prosperous enough to support high standard of living for its people, and therefore will no longer gave high wages.
So what will happen is that industries with high labour content may shift out to regions with low wages, but industries with high automation and low labour content will continue to grow in highly industrialized regions. For example the work of assembling personal computers and other electronic equipments may be done increasingly in low wage regions, but the highly automated manufacturing of computer chips and other electronic components is not likely to shift to low wage regions.
The growth of highly industrialized city is likely to be restricted more by the high cost of maintaining infrastructure of a big city and the high real estate prices. This will may result in shifting of some industries out of these places to nearby places. As a matter of fact government in many countries facilitate shifting out of industries from such big cities by developing new industrial estates in outlying areas with good facilities and attractive incentives for starting new pants and shifting existing ones to these areas.