UPDATE: I’ve managed to create a working version! See here.
I’ve written this excellent script that will replace specified background images with an SVG image, whenever support for this is detected. It will go through all CSS rules looking for “filename.svg.jpg” and replace it with “filename.svg”. This should be ideal for anyone who would prefer to use SVG backgrounds whenever possible.
There’s one problem: It doesn’t work in the one browser that supports SVG background images! :doh:
Since the script does work when detecting support for/replacing, say, PNG files, I can only assume this is an issue in Opera. I have thus reported this issue in the forums.
Hopefully this will be fixed before Opera 9.5 goes final, if not, it’s back to the drawing board to write a script that’s more forgiving!