The original reasons that were given for the speed limit were noise and sonic boom. Any govt regulations should only focus on noise and sonic boom. If you can make a plane with no (or acceptable) sonic boom and acceptable noise that goes Mach 85 then you should be allowed to do so.
Note that if we do get to that point there will be people who pop up with additional objections. Those objections will be the typical nonsense that such people conjur up out of their imaginations.