Would you rather fly in business class comfort for 8 hours or with less comfort for 4 hours? Almost doesn't seem worth the expense and risk of going supersonic.
I would be so much more excited about an airplane that was large enough that economy class seating was as comfortable as business class seating is today. That would be much more revolutionary.
I would also get excited about an airplane that was vastly safer than the already-quite-safe airplanes we have.
An airplane with a fail-safe fuselage that can disconnect from the rest of the plane, parachute to the ground and land (or float) safely. This could potentially eliminate fire danger by jettisoning everything flammable (gas filled wings, engines, cockpit, and whatever else).
The fact that flying is uncomfortable and still-too-scary to millions of people are the biggest opportunities for innovation that I see.
Flying at 500+ MPH is already quite fast given the size of the planet.