Hong Kong is betting its economic future on a megadevelopment spanning one-third of its territory. The multibillion-dollar Northern Metropolis project aims to turn a rural frontier of fish ponds, farmland and villages into a tech hub of cutting-edge labs and startups. The effort also will serve as a concrete-and-steel connection to Mainland China, and eventually ten other nearby cities that make up the Greater Bay Area. But as ambitious as the Northern Metropolis may be, let alone the $2 trillion economy that will include Hong Kong and its sister cities, it is all part of a much larger, almost unfathomable transformation planned for the world’s second-largest economy. Beijing foresees 19 of these megaregions spread across the country, hoping to fuse hundreds of millions of people into urban engines of knowledge and labor. But Hong Kong's experience may be a warning about what’s to come. As concrete swallows the landscape, it raises a critical question: is this the model for humanity’...