Persistent watch and implementing the feature to act like "state machine" which is mentioned in ZOOKEEPER-153<https://issues.apache.org/jira/browse/ZOOKEEPER-153>, would be great for ZooKeeper user. I think HBase would like to know all the change in zk rather than missing kind of events.
So, would we continue developing these features? It's also a little complicated to develop with zk and I think there're lots of things to improve.
