I agree. This spec looks very under developed yet and I'm not sure it actually addresses the key issue which prevents more universal adoption of end-to-end encrypted email.
The problem is and remains one of key management and humans, which becomes even more difficult because it is trying to retro-fit encryption to a protocol which has no support for it.
The real challenge for specs like this is that they mean nothing unless a majority of mail clients support them. Getting them added is going to be extremely difficult - near impossible. It is more likely we will just see people move to different comms channels which are secure rather than trying to retro fit traditional email. A bigger problem is that their spec for level 1 only deals with users using a single mail client. I'm not sure in this day of multiple devices this will be sufficient. The reason I moved to an imap based setup is that I regularly use 3+ different mail clients on 4+ different devices. I need to be able to access my email from all of these devices and this spec will fail to provide that. Level 2 looks like where this functionality will be targeted. However, the problem is that level 1 may not get the uptake/momentum needed to get to level 2.
Note that I'm not meaning to disparage the effort - it is a good/meaningful effort. However, I think it needs to mature a fair bit before any real implementation/support can be added to existing mail clients. It is likely efforts like this are what is needed to work out a better solution, but this spec so far seems to lack some meat. It needs to provide more detail on exactly what the key problems are which prevent automatic end-to-end encryption of email and how this spec will address those problems.
Tim