I'm no aero engineer but it seems to me that the technical challenges here are myriad and complex. Hi-temp body heat shields. Hi-temp scramjet engine parts. All to save the weight from not carrying O2.

Why not simply build a bigger vehicle that carries its own O2 that''s a rocket? Fly a ballistic lob with maybe some added glide range. Forget the complex holy grail of hypersonic scramjet engines. How expensive is several added tons of O2? This solution would be orders of magnitude cheaper to develop with higher operating costs reflected in the fuel costs but maybe engine maintenance of a simple rocket engine vs non-existant scramjet engine) would save operating costs.