There are several OpenNMS features that register event listeners and react upon the reception of an event.
When we're talking about hundreds or thousands of event definitions that require certain action, it is really hard and tedious to put all the hundreds or thousands of events on a XML configuration file like Scriptd's config.
If we have the ability to add custom parameters to events, we can define rules and/or actions based on these custom parameters when the event is received.
That way, the configuration files will be incredibly simple, and the filtering is done inside the listeners based on these optional parameters.
In order to support this feature in OpenNMS we need code changes on the event generation.