In 2010, when Ronald W. Wackrow was about four months shy of completing the rescue of the troubled 6.5-million-sq-ft Cosmopolitan in Las Vegas, his boss, Related Cos. Chairman Stephen M. Ross, suggested his next assignment: Relocate to the East Coast to steer design and construction of the developer’s 17.5- million-sq-ft Hudson Yards—a 26-acre mini-city primarily sited over the Long Island Railroad yard on the far West Side of Midtown Manhattan.