Or just use a tug, which everyone has everywhere, 99% of the way

The taxiing was bad, but that wasn't the worst of it. To go from subsonic to mach 1.7 the Concorde used reheat ("afterburner") that just dumps fuel into the already hot exhaust. This is not particularly efficient. Then from 1.7 to mach 2 it didn't need reheat, and at mach 2 it was quite efficient of an engine design.

Safran showed a POC of this a couple of years ago at the Bourget airshow, but i have no idea why it hasn't taken on - their pitch was pretty good.