I don't know enough about the resources needed for something like this, but definitely like the idea of it. I did notice that there is no such indication on the Tags page, either, so doesn't surprise me that there is probably some hurdle here.
I'd be all for some sort of visual indication w/o the count. All Discussions makes a pretty good distinction between discussions w/ unread posts and those fullly read. In addition to the binary indicator (i.e. unfilled/filled quote bubble), it also boldens and blackens the text. I think I'd like to see some sort of strengthening of the category (in addition to any binary icon) to mirror that. Whether that is a inset box-shadow/border (matching the text color) as shown above or a lifted bar or something else, I don't know.
If you do opt to go one of those routes, this is the CSS I applied here to mock that up…
/* for the lifted bar */
box-shadow: 0 2px 5px 0 rgba(0,0,0,0.58), 0 4px 10px 0 rgba(0,0,0,0.45);
/* for the bordered bar */
border: 2px solid rgb(41,106,127);
box-shadow: 0 2px 4px 0 rgba(0,0,0,0.18), 0 3px 10px 0 rgba(0,0,0,0.15), inset 0 0 0 4px;