OK.  I've been talking with @ruimalheiro about design as well; in these cases, it would be helpful to discuss together as a group, to stay on the same page and have the same direction.

How could one do this by "subclassing the message back-end"?  It's a file-based API, not an object-based interface.  I sent Rui a demo of doing this by creating a new module, importing all Django message functions there, and overriding a subset.  Related to that at all?