I disagree. To quote RFC 2046:
An additional parameter, "CONVERSIONS", was defined in RFC 1341 but
has since been removed. RFC 1341 also defined the use of a "NAME"
parameter which gave a suggested file name to be used if the data
were to be written to a file. This has been deprecated in
anticipation of a separate Content-Disposition header field, to be
defined in a subsequent RFC.
The Content-Disposition work has not moved to RFC status yet. Thus, the
"anticipation" is a bit premature. Note that "deprecated" and "obsolete"
mean different things.
FWIW, the content-disposition specification was originally kept off the
standards track because of unresolved issues surrounding how to specify
character set and language information for parameter values. This issue is
resolved now that draft-freed-pvcsc-03.txt has been approved as a proposed
standard. The new content-disposition draft, draft-moore-mime-cdisp-01.txt,
which references draft-freed-pvcsc-03.txt, is now finishing up last call, and I
have every expectation that the IESG will move it to proposed standard the next
time they meet.
As such, I think the expectation should now be that content-disposition will be
ready for use, especially given the time it will probably take to get
S/MIME out the door.