Jay,
good! I hope you publish the way you use the Content-ID and what
property you depend on in the Content-ID in an RFC, so that we can
avoid walking on each others' toes, reinventing the wheel and so on.
I basically think Content-IDs are a good idea, but that specifying
the syntax first and the use later is a backward way to do it.
So, I think Content-id: should have been defined in *your* RFC,
not in MIME. But it's a grumble now - let's keep it there.
(AND let's keep them globally unique....)
Harald A