We discuss the following plugins which were recently developed (based on M 3.2!) and are currently under internal review:
1) ownCloud repository plugin (file copying is feature complete; linking is a prototype based on creating a public share in ownCloud via their OCS API).
2) Collaborative folders activity module that creates owncloud folders based on Moodle course groups. Those are actually shared with members (i.e. their ownCloud accounts) privately, so that no accidental data leaks happen. Uses a "Moodle system" user in ownCloud to own and manage shares.
In order to achieve passwordless integration we developed an OAuth 2 server for ownCloud, which is now maintained by the ownCloud core developers.