Didn't see this when I searched...
While in Dual window mode... would be great to be able to highlight in the WYSIWIG window and see the line in the MD window high lighted... that way if you are reading in the WYSIWIG window and you realize you need to make an edit you can get oriented in the MD window to make the update.
A further enhancement would be to allow us to edit directly in the WYSIWIG window while in Dual window mode... I think saw a request for this.