A rare revolt by a Saudi tribe has spelt fresh trouble for a planned Red Sea megacity, a linchpin of the crown prince's economic vision already beset by low oil prices. The $500 billion NEOM project, set to be built from scratch along Saudi Arabia's picturesque western coast, is billed as a futuristic cityscape evocative of a sci-fi blockbuster - with everything from flying taxis to robot-maids. Economic analysts have ...