Quick update: now that it is possible to trigger automations based on changes to rich text fields, it is possible to create a fairly complete ‘watcher’ functionality.
You can create a to-many relation field linking a database to the User database, and then define an automation that will trigger on any field change, and send a notification to the Users who have been added to this field.
Couple this with the ability to notify when Comments/References are added, and I think it becomes pretty usable.