At that speed, why worry about stealth?
First off, this is the second flight of the Waverider, the first one only partially successful and flying roughly 3 minutes at speed before developing problems and losing thrust.
Secondly, at hypersonic speeds, stealth is totally unnecessary as any tactical radar would detect it far too late to respond and even strategic radars would have difficulty detecting a shape meant for such speeds. External stealth technologies could create too much drag that would destroy such a ship in flight. I have no trouble with the idea of hypersonic flight, only with the idea that it even needs expensive stealth technologies.