Lay flat preceded the Concorde. More than that, it was caused by it. "In 1977, El Al announced plans to reconfigure its aircraft with a small first class cabin and larger business class cabin on the assumption that most transatlantic first-class passengers would shift their business to the Concorde" [1].
EDIT: This is all wrong.
> Relatively few people are really in a situation where the few hours in a comfortable plane are worth $$$$
Business class is where airlines make the bulk of their profits.
Business class mostly started up as an offering for, well, business travelers who could give the appearance of being frugal relative to first class while still traveling comfortably. What's happened over time is a lot of dedicated first class seating has gone away and business class has been incrementally upgraded to something that's mostly much better than old-fashioned first class ever was.
> Relatively few people are really in a situation where the few hours in a comfortable plane are worth $$$$
Business class is where airlines make the bulk of their profits.
I wasn't clear. Yes. Lots of people will pay extra for business. I was saying I'm not sure how many of those will then spend 2x or more for a bit more speed when they're already comfortable.
ADDED: This article suggests lay-flat came in during the 1990s which sounds about right to me: https://thepointsguy.com/2017/05/evolution-of-business-class... I definitely remember flying business class transatlantic in the early 90s and it wasn't lay-flat.
You're 100% correct--my bad.
Yes, longer distance flights are, well, long but then you have a whole other set of engineering challenges to do those routes nonstop supersonic.