This proposal needs to be sent back for further consideration, either
by a
WG, or at least by some mailing list of those with knowledge of the
format.
It has just missed too many opportunities, including the opportunity to
document the mbox format once and for all (and warts and all).
uh, no. this is an application for a media-type. it's not trying to
define the mbox format, it's just trying to define a label for the mbox
format that can be used in contexts where MIME media-type labels are
required. the intent is clearly that this label should be usable with
the variety of mbox files that exist, not with one specific variant of
mbox file.
trying to write a definitive specification for the mbox format is not
the same thing as trying to define a label for that format. nor is it
the same thing as trying to document existing practice. many authors
and groups get these confused, with frequently unfortunate results.
however I don't think this should be up for PS, as the standards track
is intended for protocols that can be subject to interoperability
tests, and this is just a label. Informational seems more appropriate
to me.