> I do agree, but pervasive encryption like GPG still leaves plenty of
> interesting metadata around..
True enough. But pervasive encryption of the sort I described is low hanging fruit that by any sensible reasoning should have happened at least a decade ago. Yet there are zero Free/Open Source email clients that implement the nearly frictionless encryption I described. Not even the one in emacs.
When you see something that makes zero sense you must are generally safe to assume you don't have all of the facts, and that it would make sense if you had them. Which leads to the next step of trying to guess which facts would best fit the observed data. Someone or something is very quietly but very forcefully suppressing the technology. Since US restrictions on things like libdvdcss and PGP/GPG have had little impact it has to be bigger than the US government.
> Sending an email that you can be confident is anonymous is
> much more difficult than sending an encrypted email.
Actually... that is a pretty trivial problem. Make regular broadcasts to Usenet of on topic (to ensure wide propagation and retention) binary posts into high volume newsgroups with encrypted text included. Good luck figuring out who the 0-n persons in the world who has the right key to read it are.