David, one small point. Your quoted text cited Mime as not listing
support for Unicode. While this is strictly correct, it also is
misleading. The Mime document chose not to attempt any sort of
extensive support list. It explicitly lists a very, very minimal
set and refers, then, to the IANA for registration of any additional
character sets. Hence, the question is whether there has been attempt
to register Unicode with IANA for Mime.
I gather your documents are likely to be candidates for just such
registration, which is good.