Yeah, that looks good, but it would be nice if it had a way to specify different resolution copies of the same image for the future when we have varying screen sizes and varying ppi.
Good proposal though, and hope that this takes off.
You know, there used to be a 'lowsrc' attribute for the image tag. (A lower resolution image, which would be downloaded and displayed before the download of the 'src'-image file.)
It apparently is ignored by most browsers now and no longer allowed in HTML5.
I got a bad feeling about this img tag - what if everyone just uses it to post pictures of cats and people making duck faces?! the internet might be flooded with useless content!
Can't you just scale down to half-size an interlaced gif/jpeg and have the browser intelligently decide to stop downloading once it is at sufficient quality?
Good proposal though, and hope that this takes off.