I’m no aerospace engineer but supersonic flight, no matter how technologically advanced we become, will always remain incredibly fuel inefficient because of fundamental laws of fluid dynamics. A supersonic aircraft would likely remain a niche market, never replacing our current transonic passenger aircraft. I’m betting the tickets would be prohibitively expensive who isn’t in the top 1% or paid for by a government agency.
The upper atmosphere would probably have less drag, but the lower speed of sound at high altitudes would exacerbate the issues of supersonic flight and require specialized, expensive aircraft. It may become more efficient, but I still see it as mostly a niche market.