The SR-71 is half-century old technology, according to Wikipedia, it was brought into service in 1964. It was decommissioned in the last years of the Twentieth Century. Is anything in place to replace it? Or have we reached the point where the technology is reaching the point of diminishing returns? That is, we might be able to improve aircraft performance somewhat, at enormous cost, but there is no conceivable mission which would require that additional performance.

There are already many aircraft performance records which are still held by planes flown in the 50s and 60s. This may reflect natural limits imposed by the laws of physics, or simply that development has concentrated in other areas with better payoffs, such as avionics, stealth, advanced weapons and defensive systems, etc. Other areas which are probably being exploited now may include VTOL, reconnaissance miniaturization (aircraft which simulate birds or even insects), drones, disposable or expendable remote controlled planes that vaporize in enemy airspace when their mission is completed, making the return flight unnecessary.

We may have already passed the age of geek porn aircraft. They may have reached their natural upper level of developement.