I don't think that changing image/postscript to image/postscript-version-foo
will help the PostScript writers' problem a bit. For the case of
PostScript, we will certainly gain experience as to how to create messages
that are interoperable that we might want to document later, but it won't be
necessary to label the new messages any differently, since old postscript
interpreters will presumably read them just fine.
I agree it doesn't help the writer much. I believe it might help
readers. It might help a gateway decide how to deal most reasonably
with an old format vs a new one. That's the whole reason for labelling
body parts, anyway. I mean, if we take the arguments being made to the
logical conclusion, why label body parts at all? I certainly can tell
a GIF from a PS from a Rich Text, just by looking. What's the
content-type for, anyway?
If a few years down the road I send out a document written in
PostScript-1998 and (mis-)label it application/postscript, then the
difference is that the recipient gets an error from his PostScript
interpreter that says it doesn't support 3-D animation, instead of getting
an error from his mail reader that says it doesn't understand content-type
application/postscript-1998. This may be less than ideal, but does it
create a real problem? (Of course, it might cause the mail reader to use
the wrong part of a multipart/alternative, but a good mail reader would
allow the user to view any part of a multipart/alternative anyway.)
You have to believe that content-type is going to be used for more
than mail, by the way -- certainly WAIS needs content-types, Internet
Anonymous FTP Archives will want to indicate files by their type, as
are a number of other network information services. Unless you think
there should be separate IANA registration for WAIS content-type vs.
IAFA content-type vs. MIME content-type?