SGML (was Re: simplemail draft RFC available)

I'm interested in looking to incorporate SGML.

>                                  What other markup languages would be
> useful for metamail?
Is any one addressing on this?  I've seen a few scattered comments
about SGML but nothing to indicate work in this area.  So I'm taking
this opportunity to visit this issue and ask.

        What has been done to add SGML to MIME?
        Who is doing it?
        Who is interested?

I'll be glad to collect answers and post the results.