maybe we could manage notifications via security policies. then it would be easy on class and attribute level to define what can be sent out. what do you think?
same could apply to rss feeds, templates and the like.
xowiki policies make only one step in this direction, one could certainly bind some actions to the identified situations. However, this is a limited form (maybe still useful), where the publishing part (one should be able to publish event types, for which users could subscribe) and the user subscription part are missing. one could probably use the notification part of OpenACS.