Have they figured out how:
(1) To make a tube that sags just a few millimeters between pylons? Hint: A 1-inch thick steel tube sags several inches between those pylons.
(2) How to get people into space suits? Even the Air Force doesn't let pilots, even in wartime, sit in a plane at 70,000 feet without a space suit.
(3) How to get a common-carrier license, for a vehicle and tube without emergency exits?
Those are all pretty hard show-stoppers, and they seem to be working on everything but.