Let's not forget the concord was shut down mostly because one of them ran over a 17 inch bit of titanium that sent pounds of debris flying at the plan at 500mph rupturing a fuel tank and causing it to blow up. The next year some a-holes flew into buildings in NY and the pentagon and put the airline industry and economy into a tailspin.
I think that crash was more the excuse they were waiting for. Economically, it was past its prime, a prime at which I do not think it ever brought in much money, if at all. http://en.wikipedia.org/wiki/Concorde#Operational_history, for example, claims "By around 1981 in the UK, the future for Concorde looked bleak. The British government had lost money operating Concorde every year, and moves were afoot to cancel the service entirely". It also says "It is reported that British Airways then ran Concorde at a profit, unlike their French counterpart", so there may have been years it was making a profit, but Concorde was flying for prestige, not for the money.
Of course. Concorde was shut down for economic reasons.
But it was also the first interaction of the concept, and built with very inefficient technology. The Space Shuttle flew for the first time 5 years after Concorde began commercial service.
How many improvements have we seen in commercial aviation technology: better engines, better aerodynamics (and CFD), lighter materials, fly-by-wire
If a new SST is ever designed it will probably sill be inefficient, but ahead of the original Concorde. You probably wouldn't need it to go Mach 2 for example, maybe Mach 1.5 saves enough time on a trip to justify it.
Not to mention the issue that Concorde had Economy class seats with First class price.
There is also the related problem of reducing the sonic boom. One of the reasons why the Concorde was so expensive was because there are so few routes that it actually makes sense to use the Concorde on. Even today, we can add a few more routes that makes sense (thanks to China's growth), but even then, the limited route options would mean a relatively low demand for airframes, thus an inability to take advantage of economies of scales (which are super important in aviation, since R&D costs so goddamn much).
Accelerating the human body to mach 20 has its own set of problems. Namely, the g-force involved. A mach number is dependent upon altitude, but they mention 13,000 MPH in the article. This is a little bit slower than the orbital velocity of the Space Shuttle (around 18,000 mph), but at these speeds, rocket launches are the neighborhood we're operating in.
Wikipedia says Shuttle astronauts experience around 3 Gs. This isn't intolerable, but g-force tolerance is heavily related to time spent at a specific level. Astronauts are screened for tolerance to g-forces as part of their selection criteria. It is unlikely that the general public would ever ride in aircraft that subject passengers to the forces commonly felt during the launch of an orbital vehicle.
