The motivation of this document is not clear to me. Using mailman as an
example, the unsubscription process is as difficult as the subscription
process, so I don't really see what's the problem that is being tackled
here. i.e., why unsuscription should be easier than it currently is.

Besides, I think that, if published, this document should specify what
are the POST arguments that must be included, and how the opaque
identifier should be generated. That's key to assess the security
considerations of this document.

Finally:
The document misses the consideration that, if an email is forwarded
with full headers, the recipients of the forwarded message would be able
to unsubscribe the original recipient of it, whereas with the normal
List-Unsubscribe, he couldn't.