Many years ago Barnes Wallis gave a talk at my school, some of which I still remember. I recall his comments about hypersonics being dependant on materials technology that could withstand the stagnation temperatures involved.
He mentioned Concorde, almost with a regret that the aluminium derivative chosen automatically set the operating limit of the airframe. Even if the Olympus engines were improved it would be of no advantage. Limit would also be around 60,000 ft as altitude temperate starts to rise again above that.
There was also a comment about US plans for M3+ airliner with a small joke about having to use heavier alloys for the higher temperatures and what with overpressure being proportional to mass, not many greenhouses would survive.
It feels strange now having sat through his comments at the birth of supersonic commercial aviation to think that it is possibly already over
