This might be a bit of a difficult one, but would it be possible to enable people to use inline CSS in posts? I mean it already works in the editor, but it just gets stripped out when you try to post it.
Or at least it did when I was messing around earlier but then I was changing something kinda niche, I wonder if more common inline CSS works..? (If it does, this paragraph will be red.)
Obviously there will be some bits of CSS that wouldn't be permissible (position:fixed for instance), but it could let people make more interesting posts.
EDIT: Interesting, so it does work for some things. Just not overflow, which is what I was trying to alter originally.