you know how google docs (the most popular example i can think of) has this option that allows you to collaboratively work on documents?
basically what i was thinking about, except in the form of a chat. as the user types into the input box each letter is sent to everyone else and added on to the current message until the user presses enter, so it's like a regular chat except everyone can see when and what you're typing.
it allows for dynamic roleplay concepts such as being able to perform against actions as you see them happen, and to be able to actually interrupt others in a conversation.