I was thinking that the way that we should do preview is by saving a thumbnail using the freedesktop.org standard for thumbnails when the user saves. Then we would get a preview the next time we got it open, we would be able to use our renderer (versus librsvg's), and we wouldn't have load a full SVG file every time someone clicked on the wrong file in the file dialog. Thoughts?
I like the idea, though in my experience these thumbnails tend to go out of sync and just generally get in the way of things. Also what if a user move the file to another place and (that's to be expected) forgot to move the thumbnails? For this situation, as well as for old files, we'll still need to render the svg on the spot. So this approach won't make the open dialog code much simpler, though it will make loading thumbs much faster in a typical situation.