CouchDB Backend
OK so CouchDB is the new golden boy of the database arena, but for something like Moin I believe it could be an appropriate document storage engine, and comes with the bonus of built-in replication which could allow for changes to be made on any replica and sync up eventually through the inbuilt conflict resolution. It might facilitate some already desirable features and allow for some new handy ones.
Feel free to contribute a backend for moin2. Be aware that stuff there is quite unstable, though.