If one day VTOL aircraft are more practical, even cheaper than conventional planes, the size of the airport can shrink dramatically. It's too early to tell if

If one day VTOL aircraft are more practical, even cheaper than conventional planes, the size of the airport can shrink dramatically. It's too early to tell if experiments like Lilium are successful (http://www.theverge.com/2017/4/20/15369850/lilium-jet-flying-car-first-flight-vtol-aviation-munich http://www.theverge.com/2017/4/20/15369850/lilium-jet-flying...) but that could completely upend the entire aviation industry if proven more cost-effective.