One thing I think about is about that technology from the 20th Century: the vertical takeoff. It is the fact that planes, instead of requiring multi-mile runways, takeoff almost vertically, like helicopters.
As I said, this technique exists since a while, but now it is a bit deserted by aircraft manufacturers, because it didn't worked out great back in 20st century.
However, the future will overcome new challenges, and one of these challenge is airport's size. While terminal critically limits the size of an airport, the number of runways and of possible pathways for taking off or landing is also a great limit factor. So we will see development of this someway old technology to the future, or will it stay as it is?