Hmmm, I'm not sure how I feel about this. On the one hand it's neat, but I wonder how much extra information this adds. For me it would say something like (4/79), which does not really add that much information for me. I think just displaying the amount of tags could be sufficient.

In what way do you use this info?

Also, if you have any other improvement suggestions (or, even better, PRs) for the tags panel I would be estatic, I've been quite unhappy with how it's implemented. It's too obscure (needs like 4 clicks to get there) and having white and blacklists separate doesn't really make sense to me, i'd rather see something like "+#tag1 -#tag2".