Attractive backgrounds
I would like to suggest more personalised user features.
Change colors of bubbles and backgrounds. Be able to shift the overall displayed emoticon colors to personal taste. Add backgrounds for other users of a group chat or forum to access.
If possible allow for development of scripts to animate dynamic backgrounds, but strictly limited to the background area of the chat and bubble boundary outlines, up to the user to invoke. If this were possible it could add features that other messaging services don't have.