This is already possible, you simply have to hover over the chat icon to see them. The chat icon starts flashing when messages are waiting in galaxy view, and they will be shown automatically when you switch back to main planetary view, or will be visible when you hover over the chat icon in the galaxy view. The reason for not popping them up automatically in the galaxy map is that it then would make 1/3 or more of your galaxy map completely obscured and unusable when anyone was talking.