Remember that the biggest technical challenge to passenger supersonic flight is hacking Congress. People really don't like plutocrats in private jets cracking their windows and scaring their dog.
That's been the status quo since Concorde. The problem is it's hard to make a supersonic jet that has decent subsonic performance, you kind of have to pick one flight regime or the other to optimize for. And the market for business jets that you can only really fly transoceanic is small.
