CA Risk/History

This seems to be missing the fundamental vulnerability: there are hundreds of CAs each allowed to make certs for any site.

At the very least, there should be a system where a site can safely declare which CAs are allowed to sign certs for it, once one of them signs for it. Otherwise, every marginal CA added decreases security. Some of the pinning options work for this (cert/ca pinning, vs. key pinning like in Chrome), but then you're exposed to "registrar blackmail risk", or issues when a CA just goes out of business or something.

This is all sort of a problem for https server certs, but really destroys the utility of the system for s/mime or any client certs other than internally issued.