Well, that's probably not going to work in practice though because site owners have no way of knowing what type of image a given avatar will turn out to be. We need to somehow set a size because site owners may not be setting the "height" and "width" attributes on their <img> tags.
(Also we need to produce square images, regardless of what users upload, hence the cropping.)
So I think we need:
- a way to "squarify" uploaded SVGs (some kind of cropping?)
- a way to specify dimensions inside the SVG so that browers display the correct size
- a way to validate uploaded files (xml validator with a schema definition?)
And optionally (but would be very nice):
- how do we optimise / minify SVGs? At the very least we could strip out comments. Can they be gzipped?