Shared libraries are great but it's very hard to know when a colleague has added, removed, moved, highlighted something shared.
The important features that I think are crucial for Notifications are as follows.
Create a comprehensive log which details any additions, deletions, moves to Lists, annotations added when by whom etc.
Email notifications to members of shared libraries when one member makes an addition/change. (Can be toggled on/off per collaborator)
Integration with tools such as Slack to notify Papers users common to a Slack of changes. Not exactly sure about how to implement this suggestion but notifications within Slack seems potentially helpful. (Can be toggled on/off per collaborator)