There is no engine that will make economic sense for either the engine manufacturer or the airline operator based on the technology we have.
This was always a fools errand.
This was always a fools errand.
Which is it?
There are so many foundational issues with low supersonic flight from a usability perspective as well (time zones are not your friend for some of it), that lots of routes can only command a premium in one direction.
You have to make so many rosy assumptions to even believe this makes sense if someone was willing to pour billions into engine tech - and still maybe have no options that are commercially viable. It’s also a nightmare from an environmental perspective.