Boeing doesn't need a big jump in speed to make the Sonic Cruiser (or Supersonic Cruiser) to be successful.
Superfically, the 0.98M aircraft is really not much: 15% increase in speed over the current generation of commercial aircraft. However, its potential to increase productivity is immense. In the best case scenario, an airline can use one aircraft to serve a daily US West Coast trans-Atlantic flight instead of the current two. That's a 100% increase in productivity. The 15% increase in speed just happens to be enough to allow airlines not to idle their aircraft on ground as often as they do now. Nowadays, good airlines can average around 12-14 hours of utilization of their long-haul jets. With a .98M aircraft, it has the potential to increase daily utilization rate to 16-18 hours (there are many examples similar to the US West Coast trans-Atlantic flights). Accounting for the 15% increase in speed, this is equivalent to 18.4-21.6 hours of utilization of a .80+M aircraft. This means airlines can increase the productivity of each aircraft by an astounding 50+%. Would I mind paying 20-30% more money for fuel (which increase the unit cost by about 5%) to increase the productivity of my aircraft by 50%? Of course I will.
Just take a look at how turboprops replaced piston-powered propellor planes, how turbojets replaced turboprops. You don't need to fly a whole lot faster and higher to be successful. The basic premise of a .98M aircraft is extremely sound. Don't be fooled by that small 15% increase in speed. It actually can be very valuable.