The Sonic Cruiser wasn't a stunt, it was floated by Boeing, but its the wrong plane for today's market, no real need for it.
One problem with supersonics, aside from outrageous cost is the scheduling time, if you have a long enough range SST to go LA to Tokyo, you either have to leave at an ungodly hour, or land at an ungodly hour!
BTW, Airbus just got an order of 60 A350's from Qatar Airways, who has also ordered 20 777's. They still have a 747SP, but I think its a private plane for the royalty, must be nice.
The Sonic Cruiser wasn't designed to travel at supersonic speeds. Boeing set the max cruise at .98 Mach. The aircraft was intended to carry 250 passengers at 40,000ft and have performance equal to most efficient aircraft in its passenger class. However, the work stalled in late 2002. The went as far as naming a project coordinator and assembling a project team. However, that was as far as Boeing went with the aircraft.
It would have been great to fly in the 747SP , I never got to fly in one of them, but, I got the fly in 6 747-400 , and not sure if it was 747 100 / 200 / or 300 .. but the interior was defiantly from the 70's, so ? I am guessing it was a 747 200.