One of the central and most useful features of Notifications (Echo) is tagging users.
One thing that is missing there is a proper way to tag groups of users. There is a hack that can do it: a template that includes links to all the user pages.
Such a hack is used in the Hebrew Wikipedia to tag all the admins. Technically, this works, but as an admin, who is included in this template, I find this way of tagging me very inconvenient. In practice, this usually happens in discussions that are barely related to me. When I'm trying to understand the context and the reason for being tagged, I'm trying to search the discussion for my name (Ctrl-F), and I cannot find it. After this happened several times I learned to remember that I am also a "member" of this "group", so I check whether I am tagged this way, and it's still inconvenient.
This also doesn't scale: There is now a proposal in the Hebrew Wikipedia to create more user groups in this way. If this is done and I'll be included in any of these groups, I'll have to search for the name of each group to understand why was I tagged.
The general idea of making groups of users according to common interests, participation of wiki-projects, expert knowledge, etc., is excellent. It's a feature that MediaWiki sorely lacks—currently such things are done using categories, userboxes, templates, plain lists, etc., but none of this is really robust. Having such a feature that would be properly planned and designed could really improve collaboration.
As a possible hack till then, I can propose for the case of being tagged as part of a template is to show a different notifications: Instead of just saying that I was "mentioned", say that I was "mentioned as part of the group TEMPLATE NAME". It's far from perfect, but would be more convenient than the way it currently works.