They (US) had thrown Considerable amount of testing and money for Scram jet Development. Nasa X-43 was an example and they have been carrying out tests for the last 40 years on actual flying prototypes. We have Just begun. Boeing's X-51 Program began testing in late 2006, and They have completed a full program on it.
No Nightmares there, Also US Aerospace research is Primarily Carried out by US Air force, Which has access probably the Best research facilities, Huge Military industrial Complex and a Black budget of $0.4 Trillion (That's India's 20% of GDP) . I would draw conclusions rather cautiously.
Here is something from Wiki :
On 1 May 2013, the X-51 performed its first fully successful flight test on its fourth test flight. The X-51 and booster detached from a B-52H and was powered to Mach 4.8 (3,200 mph; 5,100 km/h) by the booster rocket. It then separated cleanly from the booster and ignited its own engine. The test aircraft then accelerated to Mach 5.1 (3,400 mph; 5,400 km/h) and flew for 210 seconds until running out of fuel and plunging into the Pacific Ocean off Point Mugu for over six minutes of total flight time; this test was the longest air-breathing hypersonic flight. Researchers collected telemetry data for 370 seconds of flight. The test signified the completion of the program. The Air Force Research Laboratory believes the successful flight will serve as research for practical applications of hypersonic flight, such as a missile, reconnaissance, transport, and air-breathing first stage for a space system.
