A few years ago Boeing proposed its Sonic Cruiser.
It was to be trans sonic at about .95 mach.
This would save around 1 hour on London to Los Angeles.
But the numbers did not add up re. higher fuel burn and development costs, so they went for the B787.(I'll bet the development costs are about the same now).
You could save 1 hour in the airport if security procedures and baggage claim were streamlined.