can a shortcut be considered to toggle the crop while in the preview window?
the thought is to offer a quick way to see how the crop will look with just one key.
perhaps pressing the spacebar might be a good candidate for a keyboard shortcut.
with this possible feature, while previewing a photo, pressing the spacebar quickly calls up a full screen version of the photo with the crop applied.
no need to fade/transitions, etc. it should behave very much like the larger preview thumbnail while in the caption editor, only in the preview window, it should be full screen photo with the crop applied.