The author thinks that the physics of Musk's original hyperloop proposal aren't going to work out, at least with today's technology -- in particular he focuses

The author thinks that the physics of Musk's original hyperloop proposal aren't going to work out, at least with today's technology -- in particular he focuses on the difficulty of building a suitable axial compressor without a major advance in technology. As a lay-person I can't really evaluate his argument. But even if he's right, I think he may be drawing too strong a conclusion. To my knowledge all of the current experimental hyperloop systems have already dropped one aspect of Musk's original proposal: instead of using air bearings they're all using maglev systems now. I am expecting that sometime soon we'll also see variants on hyperloop which dispense with the static air column in the tube and instead are designed around the idea of blasting the air through the tube at the same velocity as the car. Of course you've got drag throughout the entire tube, but on the other hand if the air in the tube is a not-quite-hard vacuum as in the original hyperloop proposal, there's maybe not that much drag when you add it all up.