I was surprised the article didn't mention Boom, which is targeting the business-class airliner tier. Their value proposition is different, and closer to Concorde: no plans for 'boomless' supercruise, but also vastly higher supersonic cruise at Mach 2.2. They haven't started constructing their airliner yet (named Overture) but XB-1, their supersonic demonstrator and testbed, is in fabrication right now.
It's clearly a submarine (http://www.paulgraham.com/submarine.html) article. The article is so light, and so full of hot air, that it practically advocates for balloon travel, not supersonic flight.
