Another approach would be more comfortable travel at today’s speeds (or even slower). Imagine boarding a plane with a luxury hotel like experience. A buffet breakfast, some work/reading in a nice library, followed by some treadmill / stationary bike time, then a shower, lunch, a massage in the spa. Dinner later before a classical concert and finally heading to sleep in a comfy bed. Then wake up and disembark at your destination.
The target audience for this wants to get into, and usually return from, their destination as quickly as possible. The trip is a means to an end. It's not unlike opting to take rideshare when your bus or train is slow.
I can absolutely see tech salespeople using this mode of travel for critical meetings. Fly out at 0600 ET from JFK, arrive into LHR at 0900 ET/1400 GMT for a 1500 GMT meeting, do dinner and such, then fly out at 0900 GMT the next day to arrive at 1200 GMT/0700 ET for a full business day. Minimal jet lag.
What you're describing is high-end private air travel (for the rich and not time sensitive) and cruises (for people looking for a vacation in a box).
Another thing might be crucial equipment. One of my friends works in the film industry, and they told me the insane dance every that goes on every set. A-lister actors, directors, and insanely expensive equipment is flown in from all around the world, and they literally often have hours of having everything in the same place, during which window they have to record the scenes, then everyone flies off to somewhere else, and the meter is ticking to the tune of god know how many thousands of dollars per hour. No mistakes or delays are possible.
He once told me of a story when some exotic piece of equipment broke, and there was NO replacement on in Europe. After a mad scrable, they did find something and they had to fly in that special camera rig thing on a private jet.
Many of the people I mentioned already travel in luxurious conditions, and the economics for luxury aviation are well-explored. It misses the fundamental issue here though. Time spent traveling is time that isn't spent setting up for an event or meeting with fans/media/business interests. You can't solve that with classical music.
It's two different problems. Yes, if you absolutely positively have to be in London in four hours to Sign The Big Contract, you'll pay whatever the Concorde replacement charges and put up with whatever experience it offers.
But there's a huge market in conventional tourists that have more flexibility and could choose from more options.
A typical tourist-class trip is going to be one day of "Travel Misery Time" followed by "Actual Vacation" followed by another full day of "Travel Misery Time".
Yeah, theoretically it might be less than a full day door-to-door, but if you're not an experienced traveler with expert experience in managing timing, baggage rules, TSA procedures du jour, and navigating the facilities, you're probably writing off the whole day of arrival and departure. Nibbling away a couple hours in the metal death cylinder doesn't solve that.
What if we said "we can swap one day of Travel Misery Time for two days of Resort on Wheels Time?" You might get fewer days at the destination, but an overall more enjoyable trip. Rail can offer that. Even today's Amtrak long-hauls offer a comfortable sleeper room, real food, and actual scenery, and no airport suffering, and there's no reason future offerings couldn't introduce other amenities (i. e. a spa car, or scheduled entertainment).
At human levels of expense, I think it's not. I traveled Amtrak sleeper on a 24-hour ride. There was no shower, so I couldn't have gone 48 hours, but otherwise it was end-to-end way more pleasant than any international flight I've ever taken.
That already exists to an extent with private suites on certain Emirates long haul flights. It is extraordinarily expensive, more than regular first class.
