Um, I really don’t have time to debate the reality of supersonic cruise engines but with a little websearching, you can find many current examples, all of them with very good SFC and decades of flight history in their predecessor engines.
Note the paragraph about “In 1988, ...Preliminary study had shown that IDF could supercruise with the new engine. ....”
In addition, the AS2 will use the GE Affinity Engine which is really just an adaptation of the CFM56 with some interesting extra diffusion provided by the second stage fan compounding and a not surprising medium bypass flow split, typical for a supersonic design point.
Nothing “revolutionary” unless you compare it to their now aging 1970s F404 designs.
So the engines are really the driving factor. The modern 3D Viscous/MDO code designs are light years ahead of where we were in 1965, which is the last time real supersonic aircraft were even attempted.
The real issue is sonic boom, and there are all kinds of good approaches now to mitigate that, but it’s an airframe/operations problem, not an engine problem.
The winner of the supersonic bizjet/airliner competition starting now will be the one with the best marketing plan, not the latest/greatest technology - the technology is there to do this.
That fact has been recognized by many and that’s why there’s so much activity: just takes the will power to get it done now.
“in 1965, which is the last time real supersonic aircraft were even attempted.”
If you ignore the F-22 and its super-cruise capability (its engines are a big part of its super-cruise capability).
I suspect you are referring to commercial aircraft. . .but since then, R&D has been on-going. . .lesson’s learned from military R&D can be data-points the commercial world can use.
The Concorde also Supercruised for most of it's flight. Yes, it had afterbruning engines, but it did not use afterbruners for it's entire time above Mach 1.
https://en.wikipedia.org/wiki/Supercruise
One of the best known examples of an aircraft capable of supercruise was Concorde. Due to its long service as a commercial airliner, Concorde holds the record for the most time spent in supercruise; more than all other aircraft combined.