I'm adding notifications to JBM2 trunk.
Currently we have:

BINDING_ADDED / BINDING_REMOVED -> when queues (or diverts) are created/deleted
SECURITY_AUTHENTICATION_VIOLATION -> when user authentication fails
SECURITY_PERMISSION_VIOLATION -> when user has not the required permission
CONSUMER_CREATED / CONSUMER_CLOSED

for CONSUMER_CREATED / CONSUMER_CLOSED, I'm adding to the notifications the consumer count for the given queue. Using this in a filter, we can be notified when e.g. there is no consumer on the queue.

What is missing is notifications when producers are created/closed since the producer concept is on the client side and the sessions is handling the messages sent by the clients on the server side.
However it'd be interesting to be notified when someone starts/stops producing on an address

I'm planning to add a few more notifications:

PAGING_STARTED / PAGING_STOPPPED -> when paging is activated
NODE_ACTIVATED -> when a backup node is activated and becomes the live node.

After that, there are other notifications that I could add but they are lower priority:

1/ notifications for start/stop of some messaging component:
- ACCEPTOR_STARTED / ACCEPTOR_STOPPED
- BRIDGE_STARTED / BRIDGE_STOPPED
- BROADCAST_GROUP_STARTED / BROADCAST_GROUP_STOPPED
- CLUSTER_CONNECTION_STARTED / CLUSTER_CONNECTION_STOPPED
- DISCOVERY_GROUP_STARTED / DISCOVERY_GROUP_STOPPED

2/ I was also thinking to add notifications when messages are expired/moved to the dead letter address but I'm not sure these notifications should be enabled by default (they can potentially generate a lot of notifications):
EXPIRED_MESSAGE -> when a message is expired
MOVED_TO_DEAD_LETTER_ADDRESS -> when a message is moved to the DLA

Do you guys have other ideas of interesting notifications?

When I've finished with the core notifications, I'll add JMS notifications for resources created by the JMSServerManager:
QUEUE_CREATED / QUEUE_DESTROYED
TOPIC_CREATED / TOPIC_DESTROYED
CONNECTION_FACTORY_CREATED / CONNECTION_FACTORY_DESTROYED