Another way for the top 0.01% of the top 1% to spend their money. Wikipedia claims 12 to 18 passengers, target cost of $60 to $80 million.
Wiki also claims: "If produced, it would allow long flights for business and private travelers, such as from New York City to London, to take only three to four hours instead of six to seven."
All that expense just so the mega-rich can save 3 hours traveling from NYC to London. They wouldn't want to be caught dead in a Gulfstream G650, which fast cruises at a mere Mach 0.90.
Nothing to see here for most people. And, IMO, it shouldn't be an "aspirational" goal for anyone. This is an obscene waste of resources and is nothing more than willy-waving for oligarchs and sociopaths.