I also think it would be really useful to let users see which categories exist, even if they can’t access them. For me it would not so much be a teaser but to provide orientation.
Could you explain a bit more why this is “non-trivial”? Is it not possible to detach the visibility settings for the categories from the visibility settings for the category content?
If it is really impossible to add another category setting defining who can see the existence of the category but not the posts therein, one possibility could be to work with groups, i.e. the existence of a publicly visible group points to the existence of a hidden category. But the problem with this is that it forces you to make the group membership public. So, in a way, we have the same problem at the group level. This is particularly problematic in public forums where publicly visible groups are visible to the world. Perhaps it is easier to add add more nuanced group visibility settings on that) than to change the category visibility settings?
If so, I see two levels of possible improvement:
- add a setting to limit group visibility to logged-in users
- separate the group visibility from group-membership visibility
Oh, and what about the possibility of a creating a category page which simply lists all categories that are set to be listed? That could be another workaround for some scenarios…
BTW, this has come up before: