Recently, I noticed the Suppress this category from the homepage option on my Discourse install.
This sounds like a perfect precursor to something like an “event category,” or a category only visible while certain events are happening.
Basically, an “event category” will have a switch on it that, when enabled, will completely hide the category – allowing no access except by a direct link. This would hide the category from the Categories page, from the category selection menus, and hide any category posts from the “New/Latest/Unread/Top” sections.
Event Mode can be enabled by either using a checkmark, or by selecting a date range in which it’s enabled.