The problem I see with this is while it's nice to dream about 800 mph travel, I can't imagine that it would be feasible to construct a track or tube that could follow the terrain at that speed and still maintain passenger comfort. If you are building above-ground supports, you don't want them to be 500 ft tall as would probably be required in order to keep the tube straight enough for passenger comfort and safety.
Luckily, advancement doesn't have to wait for the average guy's imagination to catch up. Have you actually read the proposal or are you just doing the usual slashdot thing?
The guy runs two companies, one in the space business and one that makes electric cars. I'm sure he'll need to ask a construction company for advice about the pillars, etc, but is there any reason to suppose he hasn't run this past the best engineers in those two companies? I'm sure his cost estimates are off, they can only be estimates this early in a design study, but it's not like he doesn't have engineers that know aerodynamics and vehicle design.
I'm willing to give him the benefit of the doubt until real rebuttal arrives, say from someone who can point out actual errors in the proposal.