It would be so interesting(and I think not so difficult) to view in a frame on the right (or another tab in the browser) the actual position of the line being printed in the gcode file.
The current sent line could be highlighted (or an arrow in front, or a scroll, or other), and other format could be possible. (or the choice of seeing only z-positions or other...)
I think for the plugin makers, this would be quite usefull too, unless it already exists of course.
So you can see what's to come, and what has been done, and for debugging, this would be sooooo usefull.