Here's a few on the top of my head:
- Dislikes/frowny face reaction
↑ A disable button for this would be useful if someone doesn't want any frowny faces at all
- Polls? Not sure if this would be possible, would be really cool though
- Social media links
- Gradients on theme (I saw this when neospring was alive and really liked it!)
- More markdown features, such as strike-through, dashed underline, etc.
I'll reply with more if I can think of any. I just think these would be a nice addition, if added.