A service where your limo drives out to the aircraft, with all searches and paperwork pre-done, would have about the same time gain as going Mach 1.7 vs. Mach 0.85.

Underrated observation. The low-hanging fruit is all in the office/home-to-takeoff and touchdown-to-office/home blocks on each end, not the time in the air. The commute, checkin, security, airport transit, boarding, and taxiing are the time-sinks worth optimizing.

That's a real service. Some airports, including LAX and London Heathrow, allow a "tarmac transfer", where the limo goes directly to the plane. [1][2] Cost is $200 to $1000. That could save an hour or more at each end.

VIP Terminal Access: Skip the standard queues and enter exclusive VIP terminals where you’ll receive expedited passport control, security checks, and personalized services, all while enjoying luxury amenities. Avoid long security lines with expedited security processing, ensuring you spend minimal time in the airport.

[1] https://limossist.com/tarmac-transfers/

[2] https://airssist.com/airport-tarmac-transfer-service/

private jets already solve these problems.

Which already is a bad signal for the article's argument. We already have a way to significantly reduce that travel time and it's a niche.

Could Boom Supersonic or whoever actually survive selling only to a hundred Taylor Swifts? How are they going to keep the lights on for the 30 years those jets fully saturate the market?

And probably fewer regulatory hurdles (and I don't mean that because they wouldn't be considerable...)

But for the private jet market, the reduction would be huge. They're already paying a premium to save time. The top end will pay an even larger premium to save even more time.

I agree with you that for commercial, anything other than super long haul (which is technically very hard), the time saving advantages are much less compelling.