FWIW I don't think you've answered the "What to use instead, then?" question. I agree there are platforms that are much tighter on security compared to x86 (say, iphones seem to fare quite well), but I don't see how I could use that for my "regular" work. For that, I think Qubes is "reasonably secure" but hopefully it'll get better.
Of course, if your threat model includes guys from NSA/FBI/Mosad, then perhaps it's not enough. But then again, iphone may not be enough either.
If you need a workstation that is hardened against the big boys, I doubt such a thing exists, and it never will if people keep putting all of their hope in the next band-aid. It is also a damn shame, since it's not like this is a problem that needs two more generations of pure science to solve.
Hell, the B5000[0] was safer than the things we run today, and people didn't stop having better ideas about computing in 1961.