Actually, Boeing and NASA did a study that concluded a supersonic airliner capable of flying 300 passengers LAX-NRT non-stop at an average of Mach 2.2 is technologically feasible, thanks to several breakthroughs in jet engine design that will allow the plane to be ICAO Stage III compliant on take off and landing, have much lower emissions of oxides of nitrogen (which can damage the ozone layer at high altitude easily), and also have much better fuel burn per passenger mile.
The only reason why Boeing has not persued the concept further is the high cost of development: US$18 billion. But given that Airbus is about to shell out US$12 billion to build the A3XX, I think Boeing may be reconsidering their decision and may actually do more serious studies on whether it makes economic sense to build this plane.
Remember, we're talking about flying across the Pacific at twice the speed we're doing now with our 747-400's. Even with one technical stop for fuel in HNL, a LAX-SYD flight can fly from LAX to SYD in nearly half the time it takes for the 744 to fly the same route on a non-stop flight. Imagine flying from LAX to NRT in six hours westbound or five hours eastbound; this could be very desirable for business travel.
It could also mean that US East Coast-LHR/CDG/FRA supersonic travel will be very viable again. Because the proposed plane can fly LAX-NRT non-stop, this means the plane has the following advantages:
1. It will not require special exemptions for noise and exhaust emissions, thanks to ICAO Stage III noise compliance and the new combustor design. That means the plane can land at any airport in Europe with no limitations.
2. It will seat 300 passengers, which means ticket prices will not have be be outrageously priced like a Concorde ticket; the plane will likely have both First and Economy class sections.
3. With its range, every airport from MIA to BOS can be used to fly to LHR/CDG/FRA with supersonic service.
In fact, I won't be surprised that such a plane will be announced by the 2007-2010 time frame for introduction into service by 2015.