Interesting concept, and one that's probably well over due, but I get the feeling it may be a little like implementing DNSSEC or IPv6... Who knows, maybe the Snowden leaks will provide the push necessary to overcome the inertia.

http://arstechnica.com/business/2013/10/silent-circle-and-lavabit-launch-darkmail-alliance-to-thwart-e-mail-spying/

http://www.darkmail.info/