Actually there is a "realtime" shared folder with all the references for a document by default. You can get to it in Google Docs "Paperpile > View all references".
Unlike other shared folders, this page is not integrated in the main Paperpile web app though. I'm not exactly sure what the goal is in the end. But it allows for example that user A imports a reference to his or her library that has been added by user B to the document. Is this helpful?