I believe they are thinking that one is a solved problem (Jet Engine) and the other is a novel problem (Airframe with reduced supersonic noise). There has been some work done on the sonic boom problem, but not nearly as much as the jet engine problem.
They will probably just iterate from an existing engine design rather than trying to re-invent one. Just because no one is manufacturing them doesn't mean the designs are not there to be used.
Jet engine is a "solved" problem for like 4 Western companies (GE, Pratt-Whitney, Rolls-Royce, Safran) plus some Russian and Chinese state-owned enterprises that mostly do military work. These organizations guard their secret sauces vigorously. Designing a cutting edge jet engine from scratch (i.e. with competitive fuel efficiency) is NOT a trivial task.
>> Jet engine is a "solved" problem for like 4 Western companies (GE, Pratt-Whitney, Rolls-Royce, Safran) plus some Russian and Chinese state-owned enterprises that mostly do military work.
There's actually quite a few companies that make small turbojets especially for military purposes and up to a certain point, you can even DIY your own from spare parts (there are some Youtubers that have done that). That's the first tier and includes companies like Williams, usually producing <5,000 lbf engines.
Then you have companies like Garrett/Honeywell that can make engines that output tens of thousands lbf like the TFE731 for mid-range jets and fighter jets. These can power big jets but not very fuel efficiently; that's the second tier.
The next tier up is the high bypass turbofans producing tens of thousands lbf used for commercial aviation and afterburner engines for last gen fighter aircraft are a completely different story. The GP is right there are only a few players in the game. Due to scaling laws, at this point it becomes less about the design and more about the metallurgy and material science. Magic like single crystal alloys are critical here and are very closely guarded secrets because the knowledge unlocks everything from ICBMs to gaseous centrifuges to nuclear reactors.
Ha jet engine that can be certified maintained and is efficient is barely solved by GE. That’s it nobody else can make a modern commercial aircraft engine that isn’t a total money pit.
They are at least a generation behind GE and the company is on life support so I don’t see them closing the gap. Pratt now Collin’s has engines too but their commercial engines are 3-4 generations behind.
Although I think it's not going to be as easy as picking one up at the corner store, I do not think supersonic flight (which occurs every day on thousands of airframes) will compare to the level of complexity of landing a human being on an irradiated airless rock 238,900 miles above the earth's surface and returning them safely.
Edit: There are private groups that own supersonic aircraft and maintain them. EG:
They can get a hold of existing models and diagrams to produce their own copies since the patents have long since passed and been declassified for decades.
They will probably just iterate from an existing engine design rather than trying to re-invent one. Just because no one is manufacturing them doesn't mean the designs are not there to be used.