I think it's absurd to assume that supersonic flight will only be a 20% premium over coach class in a conventional aircraft with 3-4x the carrying capacity doing less work against physics and subjecting its more components to less physical stress.

If the price point comparison is (more plausibly) between business class in one of several A380/777 flights, chartering a flight and leaving exactly when and where you want if there's a group or coach class in a Boom, I think the choice is rather less straightforward. I'm not saying there's no demand - obviously Concorde filled seats - but I am saying it might not be sufficient to make a viable commercial aircraft programme even without restrictions on where they can fly.

From a physics standpoint ultra high altitude supersonic flight is not that much more expensive. The problems are mostly around economies of scale, but as soon as you get something that's competitive you will expect the price to fall quite a bit. A 400 passenger super sonic jet might use 2x the fuel per flight, but when it can make twice as many flights per day that's huge from capital standpoint.

That said, the concord was much closer to a prototype than what economical supersonic aircraft will look like. But, nobody is trying to build thousands of 400 passenger supersonic aircraft which makes your comparison more realistic.

Sure, a 400 passenger supersonic jet that only used twice as much fuel per flight but operated twice as many flights per day with comparable annual capital and maintenance costs could sell tickets at similar prices to coach class in a subsonic jet (assuming no barriers to operation on the same range of routes)

But I'd imagine there's a reason that jet doesn't exist even in the realms of the most hyperbole-filled press releases of supersonic jet ventures...