Since the discussion is still on progress on the mailinglist this site is only a place to collect some random ideas. It will also contain ongoing discussions from the Osnabrueck 4 meeting.
Here you can find the source code of a small prototype to transport pim data via DCOP. You need a current libkabc from 3.5 branch to get the transportation of contacts done. For serializing events/todos/journals I'll provide a patch for libkcal soon.
Tobias Koenig <tokoe@kde.org>