At some wikis editors may wish to form a group, such as a wikiproject. Membership is maintained in two ways: by listing members on a wiki page by hand, and by adding a 'I am a member of wikiproject Foo' userbox on a user page which adds the user to the appropriate category.
Is it possible to make it so that pinging at wikiproject page via Echo results into a notification being delivered to all its members? Each user would be able view their wikiproject membership in the Notifications tab in their preferences and untick WikiProjects whose notifications they do not wish to receive?
It is a real need. I've seen a wikiproject notification system on French Wikipedia, where you can mention a project. You add a template and that template is listed in a category. You need to watch that category's activity, which is... another problem. :)