I had a professor who used to say the Sonic Cruiser was nothing more than a diversion created for Airbus so they would not think the 787 was in development. As it turns out, there is credence to this theory lent by the fact the Sonic Cruiser was dropped by Boeing, plus the fact that Airbus is late developing a high-efficiency composite airliner of their own. The main support for my professor's idea was that aircraft aerodynamics are very difficult to manage in the transonic range. All aircraft, either subsonic or supersonic avoid the transonic range by staying well below it or else bursting through it on to supersonic cruise. To design an aircraft to "hang out" at Mach 1 is folly among aerodynamicists, but a good way to mislead anyone who doesn't know enough about it. A fake project would have been alluring to Airbus while they chased aerodynamic smoke and mirrors. Boeing has long had an an excellent fluid dynamics modeling ability, and aside from NASA whom they collaborate with, whatever they do is considered cutting edge. They probably never intended to make a sonic cruiser and the efficiency would not have been what they said it was, namely equivalent to other aircraft flying at 0.85.