I think the idea of replacing the alt-attribute by the content of img is
very good. An image used as an <img> needs to be content-related an
therefore you often could place a descriptive text into it. This would
lead us to img being only a normal HTML-element with normal content, but
the ability of specifying an image by "src".
On the problem of implementation:
<img src="borken_url.jpg" style="white-space:pre;
font-family:monospace"><span style="white-space:pre;
font-family:monospace">Test
Hallo
World</span></img>
If the browser knows the syntax, it'll render correct, if not it'll
render correct only in case broken_url.jpg is really broken. Otherwise
the text would be underneath it. So you would need to position the span
over the img.
I don't know whether it's worth the effort, but it would be a better
syntax than alt, in my eyes.
Nikita Popov