Commercial supersonic flight is dead. -There is just no way that you can get around the fact that it takes roughly two to three times the fuel per km flown to travel at supersonic speed. There are fairly fundamental reasons why there will be no significant advances in this area. A future supersonic jet transport might have a glide angle of 12:1 (concorde was ~8:1) while a modern commercial jet is over 20:1 and a future BWB is over 30:1 (some gliders hit 60:1). -The sonic boom prevents any overflight of populated areas and even if significant noise reduction could be achieved the very small constituency for such a service would still see any residual boom noise used as an excuse by the general (and envious) public to restrict or outright ban such overflight. - Exhaust emissions at 20km altitude (roughly double 10km of commercial jets) are of far greater environmental concern due to lower mixing rates with lower atmosphere, impact of water vapour as the number one greenhouse gas and proximity to the politically and environmentally sensitive ozone layer. -Technology really hasn't improved much in relevant materials or engines. Add to this the high costs of development, relatively restricted range and limited routes and you have a total non-starter.