This is not just about "text extraction", my whole point was that an alt text is not enough. An SVG document has a DOM and a navigatable accessibility tree just like HTML documents (including ARIA attributes etc). There is more that happens for sighted users too - text becomes selectable in the SVG, links are clickable, etc. All that probably needs the context of a browsing context and DOM created in an <iframe> or <object> and not in an <img> and is specced in detail. I really don't blame browsers for implementing the spec.