But even if you assume there's a viable transatlantic market for supersonic flight, you probably can't charge all that huge a premium over business/first. If your premium has to be 2x to 3x, I doubt you have a market.

Handwaving away noise issues with supersonic flight over land gets you closer to something viable. But you still need economics that aren't that different from an all business-class subsonic. (And my understanding is that British Airways had trouble making all business work on the London to New York route.