Upvote and downvote chat messages.
add some type of liking and disliking messages in chat. I feel like this is a good way to make chat experience more interactive. I know I personally prefer to read chat rather than type my own messages (unless I'm spamming) so I think that a good way to allow lurkers to interact more with chat would be some like and dislike feature. someone posts something funny, you can like it. A mod types anything at any time, you can dislike it. probably make it togglable both for streamers and viewers.
I believe this would be a good next step in improving chat experience.