Technically possible to build. But do you have to be as rich as Branson himself to buy a ticket? And if  you are, will you be dumb enough to blow that kind of money on a ticket? NYC-Tokyo is a particularly bad example: almost straight E-W across 11 time zones. It takes you a good 36 hours to readjust to that, which is effectively part of the travel time. So compared to a conventional airliner taking 13:29 average (JFK-NRT), the Branson special cuts your total time (flying plus readjustment) from 49:29 to 37:00 This suddenly looks a whole lot less impressive considering the undoubted huge difference in ticket price. The real truth is that high-speed travel only shows its full potential on long N-S routes which have only small time changes, e.g Stockholm-Johannesburg or  Toronto-Buenos Aires; and geography dictates that there just aren't that many routes like that. It is my belief that this was a factor in the demise of the Concorde, albeit not the only one (difficulty with range and fuel consumption were also serious issues.) The one exception is travelers on quick out-and-back missions who do not linger long enough to need to adjust to destination time; but this is a miniscule niche market.