I'm currently working on an integration with a SIS.
Basically I need to send a grade every time it changed so we'll have a real time synchronized system.
That it would be great to have an Event that be call every time a Grade is modified.
I think this should be included in the class grade_grade in the function protected function notify_changed($deleted)
The event content would be almost the same (if not exactly the same) as the event \core\event\user_graded. The only different will be that the event is called after every update where \core\event\user_graded is only called when a teacher update the gradebook on the grader report page.
I think this will be really useful for Moodle integration.