Aside of providing proper upgrade scripts what else would be a show stopper currently?
@daniel.pan mentioned via email a couple of days ago that the Pro edition supports PostgreSQL.
Thanks to @caniwi and his forum posts I was able to get it up and running - nearly.
From what I can tell the only component which doesn´t support the pgsql database type is seafevents?
ccnet, seafile and seahub have support for it (like in the CE) unless you use the seafile-pro-server_*x86-64Ubuntu.tar.gz tarball which seems to lack support of pgsql in general - at least this is the case for 6.0.8 so I´ve used the common tarball.
At the moment I ran 6.0.8 Pro with a mix of PostgreSQL (ccnet, seafile and seahub) and SQLite (seafevents), not ideal but it works.