Does he know of anyone in the tightly-regulated airline industry who would be crazy enough to build a completely new airframe and engine around a currently-experimental precooler?
At that speed, I wonder what accidents will look like. I respect this technology as totally serious but in case of accident the NTSB may just delegate the investigation to a Darwin prize:
Is the plane sensitive to slight variations, like a few people walking in the alley? Since at Mach 5 we can expect a 5000K temperature for the dislocated parts [1], will the pieces completely burn and disintegrate before falling back to Mach 1, effectively acting as a MH370 at each accident, by design? Can we at least have a video of that on 9gag? Or will we have to search a 5,000-km radius if we have a 20minutes uncertainty for the accident window?
With LH2 and LOx as fuel-oxidizer, whatever are the consequences of speed, they'll be over a completely pulverized ex-airplane, not over entire parts.
Also, with that to speed, I wonder how big a runway this thing would need. It would probably operate on a completely separated airport, faw away from cities.