I've almost finished designing the XML schema I'll be using for the chat system and then it's pretty smooth sailing implementing the functionality on the server. Now's a good time to suggest anything else you'd like to see the chat system doing because I don't want to have to go back and re-design anything beyond this point.
Would it be possible to use the same GUI element that displays the player on the player editor as a display picture, but just the head?
For example, when the user clicks "done" on the avatar menu (with flood protection, of course), the information about their head color, face decal, hat, hat color, accent, and accent color is sent to the RTB server. When users initiate a chat with one another, they retrieve the player information about the other user (and themselves, but that can be done locally), and it creates a small box with their head in it, much like display pictures in other instant messengers.