Ability to get count of certain "types" and "tags"

I have a couple of different counts I want to display on my site -- comments, private messages, flagged content, etc. I can set the "tag" in the Rule which is good. It would be great if user_notifications_unread_count() took an argument for "tag" (and "type" though I don't know what I would use this for) and then the query did a join on the user_notifications_messages table to produce the needed count for the tag.