I agree with Burt Rutan; hypersonic flight will be next. In an interview I recently read, he said people sometimes ask him why he thinks hypersoar tech will take off when the Concord couldn't stay in business. His response is that supersonic flight through the atmosphere will become obsolete for the same reason high-speed ocean liners became obsolete with the advent of the comercial aircraft. Once people have the option to fly across the ocean, it no longer makes sense for ships to compete for speed. In the same way, once hypersoar or trans-atmospheric flight becomes available, supersonic flight through the atmosphere will cease to be a worth-while effort.
Oh yes, another drawback of the Moller Aircar; it doesn't fly! He's never gotten one airborne, AFAIK. I think that limitation would have to be overcome before any other advances can be made.