It was widely agreed long ago that we botched the
versioning in MIME and therefore the version would almost
certainly never change.
Yes, and it was also almost certain that nobody would dare
touch US-ASCII in MIME part headers. Unfortunately EAI did
it anyway while not updating the version, claiming that all
uses are strictly limited to the message/global "sandbox".
I don't think that's true at all. The only reason we didn't opt for a
straightforward extension to allow more than US-ASCII in headers, as opposed to
what RFC 2047, is that UTF-8 didn't exist at the time this stuff was designed
and it was far from clear that there was ever going to be an acceptable
universal character set.
My impression for message subtypes in RFC 2046 was that
message/unknown is actually opaque, to be handled like
an application/octet-stream, where B64 is allowed, while
multipart is multipart, where only 7bit / 8bit / binary
counts, other CTEs only within the multipart.
Not reallly. It was a complex situation, but basically
what happened was that there was really never intention
of there ever being any additional message subtypes other
than rfc822 and partial.
And external-body - for obscure reasons the IETF announce
list still desperately tries to use it, causing my old MUA
to crash when somebody forwarded an announcement "as is".
I routinely use the external body references to pull documents. Works fine in
my MUA at least, although clicking on a URL isn't any more difficult.
I never found out what exactly the problem is. But when a
MIME access type can be erroneously registered as subtype
for about 15 years I guess that folks don't care about it.
I have no idea what this refers to, but if you're talking about a registry
error of some sort that's pretty guaranteed to be an indication of exactly
nothing. There are plent of errors that remain uncorrected despite having been
reported multiple times. IANA is doing much better in this regard now, but
there are many years where stuff slipped through the cracks.
I actually proposed message/x400-p2 at one point as a
tunnelling mechanism and got roasted for it.
Meanwhile there are a few more message/*, some in need of
updated references (1894 => 3464, 2298 => 3798), apparently
the authors forgot this. Can I simply suggest this on the
MIME types list, and submit it to IANA after a timeout ?
If you think it is worth worrying about, sure. But really, outdated
references in registrations stike me as pretty low priority.