I'd like to bump this post and second the feature request.
Some illustrations are simple enough to be shown in SVG. Having to convert these to a rasterbased format to show them on the web is tedious. SVG can solve that, but is unfortunately only supported in modern browsers.
Having an SVG2PNG converter built-in to ZenPhoto would solve both problems.
Also imagine the plugins and hacks that could be built around this feature. ZenPhoto becomes _the_ image engine for your CMS of choice. Upload a jpg, png or svg to your filebucket and show it in resized, compatible formats.
Woo!