I think that it would be useful to have the ability to insert spoiler tabs within forum posts. For those who don’t know what I’m talking about, everything you write within the spoiler would not be shown until you open it. There’s an example from another forum below (the contents of the spoiler are irrelevant in this example btw, just to demonstrate what this sort of thing looks like):
This is really useful in threads where you want to post a bunch of images (e.g. in BST or yoyo exhibition sub-forums). It makes threads far cleaner and less cluttered and saves you time if you want to find a specific post or something. It is also useful for if you want to make a really large post with a bunch of smaller sections, rather than presenting people with a huge wall of text.