Take-off is murder for high performance aircraft. It was a huge problem for the Concorde. In principle an airliner could have achieved better economics (both in terms of fuel efficiency and capital costs) if it flew a bit faster, around the speed of the SR-71, but then the takeoff problem becomes close to impossible. The SR-71, like the Black Horse, took off with a minimal fuel load and refueled in air. It seems that a civil airliner can't do that but maybe a spaceplane can.