Part of the pitch for Concorde was that an SST would have greatly reduced capital costs since it could fly at least twice the number of flights in the same unit of time. It wasn't really fast enough to do this on the routes that it flew, so this benefit wasn't realized.
A Mach 3 airliner (SR-71 class!) is fast enough to realize better capital efficiency, and can do better on fuel consumption than a Mach 2 airliner. Some fuel is spent fighting air resistance, but some is fighting "induced drag" which produces lift. If you spend less time in the air you need less lift, and fuel efficiency improves.
The only problem is that aluminum would melt in a Mach 3 airliner so you need some revolution in materials to make it practical.
https://en.wikipedia.org/wiki/Boeing_2707
Part of the pitch for Concorde was that an SST would have greatly reduced capital costs since it could fly at least twice the number of flights in the same unit of time. It wasn't really fast enough to do this on the routes that it flew, so this benefit wasn't realized.
A Mach 3 airliner (SR-71 class!) is fast enough to realize better capital efficiency, and can do better on fuel consumption than a Mach 2 airliner. Some fuel is spent fighting air resistance, but some is fighting "induced drag" which produces lift. If you spend less time in the air you need less lift, and fuel efficiency improves.
The only problem is that aluminum would melt in a Mach 3 airliner so you need some revolution in materials to make it practical.