I think what we're seeing here is the realization that bean-counters can't stop progress indefinitely and that when a technology exists, someone will develop it.

The US folded under pressure of noise/pollution issues.

We all know that with increased production of an engine or a material, the cost goes down. SST development is in the same category as computers, lcd monitors, etc. As production goes up, costs come down. Then as more manufacturers develop SST engines, introducing competition, the price goes down further.

The Japanese supposedly have some new engine designs and if they can sink some research money into a modern SST - all the more power to them.

In the 21st century human transport is behind the curve. We've perfected sitting on one's bum communication. But actual physical transport of people and goods is still not much better than 1958 technology.

It makes sense for a government to fund SST research and development. It's patently obvious to any military-minded folks that the technology will have spin-off military applications.

SST military transport would be an awesome tool for fast deployment of special forces. The SR-71 was a great spy plane and still holds records, but the technology is four decades old.

The nation that has new SST fighters, bombers & transports at its disposal is a nation that can provide rapid reaction to crisis and also has a hearty R&D program to transport goods & people faster and more efficiently.

Commercial success is all swell and fine, but the technology needs to be advanced one way or the other. Eventually the technology will be successfully exploited commercially.