The world and more importantly the wealthy are vastly richer today than in 1976 when the concord started flying, and the R&D costs should be far lower.

There’s thousands of billionaires in the world. Not all of them would buy a supersonic private airplane, but include non billionaire CEO’s etc and the market is plenty large to support moderate scale production assuming they can keep costs under say 5x what a reasonably comparable subsonic aircraft would cost.