Concord was very old technology. I am quite sure a clean sheet now

1. Would have much lower sonic booms thanks to recent research (quite a bit of it by NASA on wing geometry) and more importantly computer simulation available now

2. The engines would be far more fuel efficient

3. The flights would be able to have better efficiency in the subsonic regime as well. Just see what winglets and the like have done to fuel economy .

I fly 14 to 18 hour routes maybe 4-5 times a year on business paying 5x the economy cost and it still sucks. Breaking the flight with a connection (IMO) sucks more. My management flies such routes every month. There is a lot of revenue headroom in that fare gap for something that flies maybe 3x-4x as fast which military aircraft already do.

What will hold back the idea is conservatism among the business managers in aircraft manufactures and incumbent airlines who will "draw lessons" from a 50 year old experiment

It'd be far more efficient than the 50 year old tech, but so is the baseline tech they're comparing it with, and the market has optimised heavily for price competition (and has a lot more private jets doing exactly the route and time executives with Concorde money want) and needs speed somewhat less when it's a lot easier to stay in touch with a business whilst inflight. Ultimately there's not much to draw lessons from that suggests it's going to sell enough aircraft to recover the investment of building and certifying it (even comparatively simple niche aircraft like the A380 struggled there), which is why even Boom is now reinventing itself as a provider of turbines for AI datacentres to try to fund its development costs...