Mark - I am going to comment only on a few of the issues you raise.
1. MULTIPART cookies
Yes, this is clearly a typo in the draft. But, your definition is too
restrictive as well. Basically, a cookie should be a parameter, which
means if I put it in double-quotes in the Content-Type: line, then I can
have anything I want other than CTLs. (I want SPACEs.)
2. DIGEST
Wrong. It should stay. I've spent a long time looking at this too.
If people want to send simple digests, they should have a way of making
them rfc934 compatible, since there is a lot of things out there that
know about rfc934. Including digest to make this functionality is
hardly a burden on anyone.
3. MESSAGE/PARTIAL
In thinking about it, I have to agree that the third param should be
mandatory. The argument for it being optional is that you should allow
you to split a message in one pass, but in practice, I don't think you
can implement it this way.
4. SOUND
You've got the right idea, but you don't go far enough. See my next message.
/mtr