In the context of more complex ILL backends, in which returning an item could imply, for example, notifying an external source it is just not enough to call $req->status('RET')->store We should be calling something like ->backend_return instead, as we do with other actions, and let the plugin handle it however they need to.
+1
Could config be based on a system preference where each library could put in the statuses they wanted cleaned up and the number of days to keep them before clearing them out?