This is related to bug 2537 and especially https://bugzilla.wikimedia.org/show_bug.cgi?id=2537#c12 but not a duplicate (at least, not one in my opinion, and if it gets duped I will go have a cry).
This would have great use with the images that are always rasterized/transformed for content, such as SVG, PDF, DJVU.
This is suggested as a first step towards a full history/diff/live-edit of SVG as vaguely hinted by http://news.cnet.com/8301-17939_109-10103177-2.html
"Wikipedia users may soon get a way to view the revisions that people make offline to photos by flipping through previous versions of the images."
(And while this may not apply to SVG in particular, such a system would be pretty sweet. Especially since duplicating Wikimedia's rsvg setup is not easy, and there is no way to actually test against it without creating a permanent (even if deleted) revision to the image servers, wasting space. A gentle next step to this system would be a plain text entry field for raw SVG data previewing... )