Manifest Icons and SVG

I wonder which one would be the easiest way to improve this "messy" feature:
http://w3c-webmob.github.io/installable-webapps/#h3_favicon

so that it's possible to use an SVG in size ranges

16, "small.svg"
96, "medium.svg"
512, "high.svg"

where accordingly with the UA the right icon is shown in the right place
(little one, medium, or big once pinned/docked on bigger retina screens)

Thanks in advance for any hint/thoughts/idea/proposals/fixes ... etc

Best Regards