Have a "Used by" tab in AGOL on the contents page that shows where services are being used elsewhere in AGOL. This would be similar to the "used by" tab in Toad for Oracle so you can see what apps, maps etc need to be updated when layers change. It would be great if there was a feature that allowed you to notify users of the service that a service has changed so they don't have to be surprised when one of their apps fails to work.