Five thousand a ticket is far from "affordable" for me.
I think Concorde flights were around 10k, in 1976 money.
They are planning on using a domestic style first class seat. Domestic first is often called business/first as most carriers only have one of the premium classes.
Quite honestly, if they are able to do this at said rates, Branson will change business travel.
Why would someone travel business class on normal aircraft, when they could fly a comparable product supersonically.
A supersonic plane would have no real need for lie flat seats for a 3-1/2 hour trip.
Maybe YOU don't see this as affordable, but business travelers and the companies they work for would love it. A COACH seat, departing Monday and returning Tuesday, ranges between $2500 to $4000, depending on the carrier. The same business class, for last minute, is $6500 to $7200
Fares fluctuate daily/hourly. Sometimes Buisness class and coach are near the same price when flying last minute.
Also, when traveling for business, a company must factor in per diem.
An exec can be in and out the same day. Saving a company on hotel costs and meal costs.
Maybe for you, this isn't affordable, but for businesses...
$5K is competitive for first/business class travelers.