While we're talking about SVGs, I'll note that our current handling of the 'lang' property on image references is at odds with how HTML and browsers implement it. See https://bugzilla.wikimedia.org/show_bug.cgi?id=58920 for more details.
We can't support 'lang' in SVG served directly to browsers/renderers (which parsoid would like to do) directly until this issue is addressed. --scott
ps. WRT to bitmap embeds, I think the larger issue is whether images on common are expected to be self-contained or not. The current infrastructure assumes that they are. It might be worth thinking of the 'big picture' and allowing a more general dependency mechanism -- if an SVG depends on a bitmap hosted on commons, then thumbnails of that SVG should be invalidated/regenerated when the bitmap changes, etc.