I answered my own question here in a post below.

If I could delete my post here, I would. See my answer below for details if you're having trouble with the participants of a share not getting notified of an owner stopping it's sharing.

I just saw these questions just now. The forum bot didn't notify me these were here somehow. Answer in separate response below

Interesting sample. I'll have to do some experimentation with it. In one of his comments, he states the following: "The purge API posts an NSPersistentStoreRemoteChange notification after finishing its job, so observe the notification to update the UI if necessary." (line 104 of PersistenceController+Share.swift) But in my own experience, this was not true. That was the issue I was having that led me to the other solutions I came up with. Maybe they've changed things to fix that now, in which case my solution would no longer be necessary.

Has anybody had any response from Apple on any of these issues? I've been waiting on this functionality for a while and I'm a bit disappointed that they didn't have solutions to these problems in place already. Sure, we can start sharing some data with other users (like in the demo), but there doesn't appear to be any way to stop sharing without causing massive sync problems or crashes. Additionally, there doesn't appear to be a way for a participant to be notified that their permissions levels have changed (say, from read/write to read-only) so you can't update their UI accordingly. This means that if you change someone's permissions while they're already on a screen where they can make edits, they can continue to make edits, which causes significant out of sync issues between owner and participant. Has anyone solved that issue?