So the 'expert' could only come up with "water might not be good enough to transfer the amount of heat that will be produced"? That's not much of a hurdle, really. Start with different materials: use coolant, for starters, instead of water. Also: the vehicle is being levitated by powerful fans.
If that is the most damning evidence against the hyperloop, I'd say the idea is pretty sound.
The obstacles brought up in the article will certainly be technical challenges, but to write the entire project off as "impossible" is simply closed-minded thinking.