This list does not really follow priority.

* Implement support of CRL checking. OpenSSL 0.9.7 finally supports CRLs,
  so Postfix/TLS should support loading CRLs.

* Cleanup the "pfixtls" special logging, so that it fits Wietses original
  "per site" decision to make debugging easier.

* Move TLS based information from separate lines into Postfix's smtpd
  logging lines to make logfile analysis easier.

* Check the "info_callback" for sensitive use. I already had to remove the
  "warning alert" issued on normal shutdown. Why is a warning issued for
  a normal shutdown??

* Introduce new tls_per_client table to achieve the same selective behaviour
  for incoming connections.

* Introduce better support for "opportunistic" encryption: collect information
  about peers connecting; log warnings when the key changed etc.
  [I am not sure that I already have the best answers available.]

* Find a way to use the certificates themselves instead of the fingerprints
  to allow certificate based relaying. The maintenance of the fingerprints
  is a nightmare.