Hi Peter. Awesome plugin!
We have a BuddyPress site that allows teachers to create groups for their classes and populate them with students. It was suggested that it would be great to be able to have a student put an assignment in the group document folder and have it visible only to themselves and the teacher (group admin). Furthermore, as the teacher and student make changes and upload new versions of the document, it could be versioned.
I'm not certain how this is facilitated by the coming privacy options in the BP core, but I was curious what you thought of this idea.