I did misunderstand you at least partially, but my point stands: container queries are part of CSS and layout, and I think it’s very unlikely that they will yie

I did misunderstand you at least partially, but my point stands: container queries are part of CSS and layout, and I think it’s very unlikely that they will yield any new approach for responsive image source specifications, because making it work would require shifting waaaaay too much stuff into presentational HTML. What the sizes attribute covers is bad enough in this regard, but it’s at least straightforward to implement in an isolated fashion.