The subject of the Sonic Cruiser having supersonic capability has been discussed in another post.
The general consensus (along with remarks made by an aeronautical engineer) is that if you can get it to hit a M0.98 cruise speed, you can easily tweak the design to punch it up to around M1.25 or so. Going much faster would be inefficient, but the aerodynamics required to economically sustain a high subsonic cruise could be pushed a bit farther to get into a low supersonic cruise.
It's likely that while Boeing knows they can make travel at M0.98 economical right now, the airlines would go nuts if they can get an airframe capable of doing M1.25 or better for the same money.
"In this present crisis, government is not the solution to our problem - government IS the problem." - Ronald Reagan
Comments made here are my own and are not intended to represent the official position of Alaska Air Group