Lockheed Martin’s SR-72 “Son of Blackbird” is arguably the most important aircraft since the invention of the jet engine. Why? Because the SR-72 promises to make subsonic, supersonic, and hypersonic (below, +1x, and +5x the speed of sound) flight possible, all within one aircraft. When this technology enters the civilian sector it will make it possible to travel from New York to London in about an hour.
While this is all fascinating, and will make air travel more convenient, that is not the real breakthrough. If you can take off horizontally, transition from subsonic flight to hyper-sonic flight on one propulsion system, its not that difficult to add an additional propulsion system to the package. Add a rocket to this aircraft, and you have a single-stage to orbit space-plane.
This will be essential as humanity pushes out to settle the Moon, Mars, Asteroid Belt, and eventually the outer planets.
I feel like the problem with SSTOs isn’t the propulsion systems, it’s the fuel. But pretty badass nonetheless.