The current implementation may actually run into trouble when Redis is scaled to multiple instances. I need to do some more research to verify that. In that case, I would have to use Redis Keyspace events https://redis.io/topics/notifications. Though the current implementation saves an extra message roundtrip.
I tested the implementation to a great extend and experienced no issues when using a single Redis instance. You can use Redis in the latest y-websockets-server branch: https://github.com/y-js/y-websockets-server/tree/v10
TODO: What happens if..