I have one uber comment about the structure of this document that IMHO
raises to the level of a DISCUSS but should be easy to resolve. Much of
the sum and substance of this document (which is section 4) should have
been under the IANA Considerations section since they are really ...
IANA considerations.

Additionally, the style of referencing section numbers (and introducing
sub-sections) in RFC7252 is very confusing. Why not say that the IANA
Considerations in this section replace the entire Section 12.3 of
RFC7252 and rewrite the considerations as new?

"4.2. New Section 12.3.1 "Temporary Content-Format Registrations"" ...
seems very odd.

IOW request the authors/WG to please simplify this patch.