The conclusion of that article actually doesn't seem to be that the Hyperloop is technically infeasible - only that the original spec does have issues, and it glossed over those issues.

"I’m not saying that the problems with Hyperloop can’t be solved. Money, time, and talent can solve any problem that doesn’t involve breaking physical laws, but I wouldn’t put my money, time, or talent in the hands of someone who takes me for a fool."