Hi @Jenkler! Long time no see
I don't think we can do this right now, since visibility is handled on the category level.
It could likely be done in a plugin though, to enforce visibility on a per topic level ..
Jan 1, 2014 - 420 posts - 33 authors for example. It doesn't show the number of authors and posts in each topic for SEO purposes. This should be pretty simple to add.