The promotional material is striking: two mirror-encased skyscrapers stretching more than 100 miles across a swathe of desert and mountain terrain, providing a future home for 9 million people. In short, economists, architects and analysts are not quite sure. So extravagant is Saudi Arabia’s plan to create an urban utopia that even those working on the project, known as the Line, do not yet know if its scale and scope can ever be realised. Neom has consistently raised eyebrows due to proposed flourishes such as flying taxis and robot maids, even as architects and economists have questioned its feasibility. The...