While I know it's obviously not necessary on xenforo atm as there are only a few forums, many other forums especially big boards being imported to xen foro will have many categories that users might not be interested in and therefore will want to minimize or hide.
Is this functionality in the pipelines or possibly already coded but not in use over here?
I think being able to actual hide categories via usercp so they don't show up at all would be a nice addition . Obviously an admin can set "allow hiding of category" so users dont hide important categories used for announcements for example. This could always be an addon though.
I do not think hiding of the hole category would be logical but maybe something along the lines of if your logged in, you can collapse the category and it would save its state to your account so it stays like that even after deleting cache/cookies etc.