It strikes me that in half a century of military supersonic flight, the design and airworthiness technical challenges are well understood.
The big questions will be about emissions - noise and otherwise, for which the world no longer has the appetite to bend rules in the way it did for Concorde. In a world where billions are being spent on trying to achieve low to zero net emissions airliners, and the tolerance of any aircraft noise reduces daily - just how supersonic transport aircraft of any form will become acceptable in the 21st century escapes me entirely. I hear vague claims that Boom et.al. can be zero carbon and compliant with present noise regulations, but see absolutely no actual evidence they will. Those certainly are the fundamental challenges to be beaten, not the enjoyable and big, but nonetheless known and understandable challenges of design and airworthiness.
G