For those questioning the economics, not what you would call overwhelming though.
Supersonic Bizjet Math Makes Sense Now, Says Analyst | Business Aviation News: Aviation International News
No amount of computer sophistication can overcome this instability
You can by not allowing the aircraft to encroach the areas where the instability will manifest itself. Think envelope protection, as used in the Airbus. As I previously posted,
coupling can be ameliorated by limiting roll rate, roll duration, and angle of attack or load factor for performing roll manoeuvres
The typical high speed aircraft has some sort of roll performance limitation by flight restrictions or automatic control device to prevent reaching some critical condition from which recovery is impossible.
In essence, it's not a lot different to the relaxed stability aircraft we have now. A less stable aircraft requires smaller control surfaces, and deflections, to initiate maneuvering; consequently drag and control surface imposed stresses will be reduced and aircraft responsiveness will be enhanced. Since these characteristics will typically make control by the pilot difficult or impossible, an artificial stability will typically be imposed using computers, servos, and sensors as parts of a fly by wire control system.