Overview of projects working on next-generation secure email
github.com
github.com
That depends on your security goal. Your goal might be to check to see if a message was sent by the person listed in the "From" field, in which case WoT can work very well.
"Nearly every project here uses Trust On First Use (TOFU) in one way or another"
This is not perfect either. In the scenario I described above, TOFU may be less useful than WoT. There are also scenarios in which TOFU makes no sense at all -- maybe I want to anonymously send an encrypted message to someone, and I have no point of reference for their key.
"This is not possible with the traditional protocol for email transport, although it will probably be possible to piggyback additional (non-backward compatible) protocols on top of traditional email transport in order to achieve metadata protection."
Ahem:
My intention was to push back on the references to hipchat, campfire and so on.