RE: compressed content-transfer-encoding?

I see a problem here with making a content type (zipped) act like a c-t-e. 
Zipped seems fine for "attachments", that is, leaves in the MIME tree. But 
some of the requirement for making messages smaller would want to compress 
a whole message, which might be a nested multipart. At this point, zipped 
hides the lower layers. If we want a rule that say "you can't use 
app/zipped for multiparts", how does this become different than a c-t-e?
--Paul Hoffman, Director
--Internet Mail Consortium