I like your idea to tie the notification of a Dataform activity in Course overview with the completion setting of the activity. This will help students to see which activities still need their attention.
If students do not turn in anything, the notification should be tied to the due date. So the notification in Course overview probably needs to be tied to two events, one if students finish the Dataform activity before the due date. Then, the notification would no longer appear in Course overview. In case students don't complete the Dataform activity before the due date, the notification in Course overview will end with the due date. Can you implement such a feature with a dependency on two events in Dataform?