you could do this a few ways. What I did was to create a role called "Ingest Playbooks" with no users in it and all cases that come in are assigned to that. At the end of the ingest playbooks I assign the case to a stage (phishing as an example) and assign it to the role with the group of users that are intended.

With doing that, I do have to watch the cases to be sure nothing gets stuck there. Weekend patching as an example.