An error pseudoselector for media

It occurred to me this evening, as I was chatting on webapps about 
createObjectURL, that an error pseudoselector for image elements would 
be darn handy.

I had to use JavaScript for my project recently, because my primary 
image is a PNG but I've embedded an SVG resource as a fallback.
Well, my primary image is an SVG at a separate url, and my fallback is 
an embedded SVG... but the point remains.

It'd be swell to have something like this

#myImage::error {
  content: url(#fallback);
}

<img src="howdy.png" />
<svg id="fallback" />

I know that there are some vendor specific selectors that touch the 
periphery of this case.
They're mostly about handling the image-broken visualization.

onerror does not succumb to issues of CORS, so it seems quite safe to 
use it as a semantic with CSS.
Further, it's possible that an error will occur at any time, such as a 
low memory condition.

That's something that JS is not so awesome at handling.

-Charles