I would like to see the document as a whole, especially its consistency/rythm/harmony from a graphical point of view. Currently, on a 23" screen, it's difficult to see more than 14 or 16 pages in one double pages column (less than 10% zoom for A4 pages); given the width of my screen, I could display ten times more, if they were displayed from left to right, then up-down.
It'll be even better, if it allows to move pages (like slides in Open Office Impress, for example), but that's not my main intent.