All said about sonic boom, shock waves, and higher v speeds (therby requirement for longer runways) are correct. But to make the project Technically feasible boeing has to count on new fuel technologies as wingtanks fuel capacity does not seem to be sufficient for longrange based on todays engine fuel consumption especially at high compressability effects. Also I reckon that the canards may be helpful in slightly reducing v speeds but are going to give them heck of a problem while Taxing in to the gate and the jetty operation. One solution could be a retractable canard at the cost of higher empty weight. As far as Economic feasibility is concerened, I am no specialist but I have serious doubts. I hope Boeing or the Americans in general dont try to envisage it as a national pride like the concorde people did ( I am sure they still don't admit its economic inviability).