[Feature Request] Spoiler Thread Preview Message

Right now, threads show a "preview" message in the host channel they were posted in, and the preview message is the *latest* message posted to the thread. This makes it very difficult to make a thread to talk about spoiler topics, like a TV show episode, book, game, etc. People still have to spoiler tag everything because that preview message might spoil someone who is just browsing the main thread.

In general, I think it would be better if there was either no preview message, or if the first message of the channel was always the preview message, but a compromise would be the ability to mark a thread as a spoiler thread which hides the preview message in the host channel.