Hypersonic passenger flight has some serious weaknesses. I’m not sure it will ever make sense when there’s billions of people who need to be served and a finite planetary energy budget.

I could see billionaires doing it, and in theory they could even manage it in a green way (but don’t hold your breath). Most Lemmings don’t like the world working like that, though, and it’s not really in the spirit of comparing it to municipal transport.