Hi Murray,
do you know wether it is a military or a civilian project ? I think it was already proved that the scramjet engine works, and NASA can build it - if I remember well that is (was) the Aurora project, also the SR-71 had a similar variable engine that could work as a scramjet. Why is it so special now that Boeing and P&W is also able to build a mini airplane with scramjet engine ?
Why the developers forget we still could not solve the problem of the sonic boom ? Why they forget we still not have a material that could survive that flight under control and in "aircraft" size and shape? Why the developers think that the gap between Mach 3 (which we already achieved) and Mach 6...8 is already DONE and we do not need to cope with it ? We have not had an aircraft yet that could takeoff, accelerate above Mach 2, and then land somewhere else, ...while taking more than 10 tons of payload. It is a great achievement that we have a little engine which can "deliver" itself at Mach 6 and that is all. I am afraid this is going to be a military project for a new ultra fast and ultralong range weapon rather than a technology demonstration for future civil air travel.
Maybe I am pessimistic, but I do not see the well-thought steps in the development. I would prefer a modern and working Mach 2...3 "heavy" airliner first, which proved that we can go beyond the Concorde heritage and we are already well prepared for hypersonic travel.