It isn't clear to me that Keld's conclusion about restricting the
use of characters is reasonable in the Internet context. For one
thing, EBCDIC deficiencies shouldn't be a consideration for an RFC
based on 822 which defined US ASCII as the character set to use.
In general, the discussion here seems to be devolving in part into
one over how to encode various characters and languages. I would urge
that those discussions be left to people working on the ISO DIS 10646,
UNICODE, and other such groups.
The scope of the RFC should be limited to Internet mail concerns
such as trying to build some facilities for labelling mail encoded in
character sets which are predefined elsewhere (ISO or whoever) AND are
of interest to the Internet community. That a character set standard
is of interest to folks outside the Internet community shouldn't be a
factor. We aren't writing an ISO standard here, we are trying to
solve a real need of Internet users in an upwards-compatible manner.
I have yet to see any sufficient or detailed justification posted
here for worrying about anything other than US ASCII, ISO 8859/n, and
ISO DIS 10646 (once it becomes ISO 10646 and assumes final form).
There might be others to worry about, but I don't think that EBCDIC should
be one of them based on the historical precedent of RFC 822 selecting
US ASCII only.