My suggestion is to add a tab system above the chat text line. When we would speak on a chanel or to an user, a new tab would appear and we would only have to click on this tab to speak only to the chanel users or to the user (whisp). We would have a notification in the tab (color change or bold, as you want) to indicate that a user have sent a message.
That would be a system like on teamspeak 3. It would be more ergonomic and clearer. It wouldn't be a big add, it realy feasible.
What are you thinking about ?
I joined an image to give an example.