Many of his arguments were based on the practical difficulties of
requiring any kind of additional standardization for document format
versions in a distributed mail application.
Now that MIME is out as a proposal for mail, I still believe that
these problems should be addressed before MIME is appropriate for
database, archival and retrieval applications. In addition, the
current mechanism in MIME for external references suffers the same
problem that other references mechanisms that are based on
hostname/pathname have: files move, change in place, host names come
and go over the years.
Both these problems are not trival to solve, but I don't think they
are unsolvable.