No engine product ready for purchase or no engine that could ever be built? If the former, whatever tell R&D to go do their job. If the latter, maybe it was a scam.
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.
Which is it?