Threads feature

I would like to see a feature on threads that allows a thread to have it's messages(even the little preview) hidden until one joins the thread. I am trying to use the feature to have a text room with various threads within for discussion of different shows and games, opt-in only, so spoilers can be freely discussed without having to tag the messages as spoilers. The one hang up I'm encountering in the little preview of the thread, which shows only the most recent message in the thread, which defeats the purpose of my little experiment. I'd love to see an addition where one could add a short description of the thread to take the place of that preview, or perhaps pin a message as the previewed message.