A transportation company is betting its sleek new hydrogen-powered electric flying vehicles will someday serve as taxis, cargo carriers and ambulances of the sky, but experts say they will have to clear a number of regulatory hurdles before being approved for take-off years in the future. With six rotors on the roof and seats inside for five people, a passenger model of the Skai (pronounced “sky”) unveiled Wednesday near Los Angeles resembles an oversized drone crossed with a luxury SUV.