I think subscriptions need to be internally hooked into the state and responses of an Event. When we got subscriptions working, we saw that they only occurred when the event was generated. Here is a use case for state updates:
As a devops practitioner or manager I want to get a one way notification when an event occurs. That way I can be aware of it and take action (or not) as the case requires. I need to keep track of the state of that event, including the responses of people that the event went to. This is especially true if the event is being closed and another one opened for transfer to a different team/group.
While it is certainly possible to embed the event Id into the original subscription notification, I don't want to have to look up the 12 events from last night by URL or event ID to see that 10 are terminated/fixed, one never got a response and one is in progress.
It is also true that the Activity Update allows a user to get notified when an event is opened and when it is closed. That covers about 80% of the above (I still don't know why an event is still open). But it requires someone with developer credentials to add me to Activity Update section of the Communication Plan. One very strong point of subscriptions is that once I, a developer have created the subscription form and shared it, people can add themselves, set their own filter patterns and so forth without needed to get a developers help.
So, is there a way to get subscription notifications on the change within the event itself. Or is there already a way to do that?