>>However, the answer, to my mind, is to do it properly rather than propose a wild experiment with hand-wavy arguments as to why it would be politically easier to do. Do you really think the special interests that are making HSR so difficult and expensive would say, "Oh, do whatever you like with your tube."?

Even when done properly, HSR has most of the limitations stated by Musk. And while it is possible that special interest groups would make the construction of Hyperloop more difficult than it is, I don't think that's an argument against giving it a try.