That's the thing, though: I am skeptical that your "professional who needs a high security environment" is going to be satisfied by this. It's turtles all the way down--while I know Joanna herself was one of the folks behind the Bluepill attack, why trust Qubes to not be vulnerable to its own version of the attack? (This is obviously an oversimplification and executing such a task is nontrivial--but breaking out of a VM was thought to be a lot harder than Bluepill made it, too.)

The closest thing to an answer to that, as far as I can tell, is multiple computers. Assuming Qubes works as advertised, however, it seems as if it doesn't really scratch the bigger itch--the technology seems cool (I haven't dug deeply into it), but does it address the social/usability problem of security, even for these professionals who need that high security environment?

From reading about this, it seems as if you could have stopped at "it's a niche operating system," because to my mind it seems like professionals who need a high security environment will just have multiple computers. If a segmented system like Qubes is not going to run the stuff that your hypothetical professional will want to run (games just being an example, and one that seems to have been misleading), then why would it be preferable to just rolling multiple computers? (Cost, which is the only advantage I can think of, doesn't strike me as a significant factor to folks who are actually doing things that necessitate this sort of security.)