This seems at odds with XML's easy extensibility and the lost
overhead of using XML namespaces; to do conneg on any format that I
create, I have to write an I-D, get it approved as Informational, and
then register it with IANA.
You need do nothing of the sort. RFC publication and IESG approval is only
required for things in the IETF tree. Vendor and personal tree entries are as
simple as filling out a Web form at IANA:
http://www.iana.org/cgi-bin/mediatypes.pl
The recent shift from isi.edu to iana.org has caused a lot of delay in
registration approvals, but that should be done by now.
Ned