I share the concerns expressed here about the “sizes” attribute that’s part of the new turbo-powered img element (or “the picture element and its associates”, if you prefer). Putting style or layout information into HTML smells bad.
This is a concern that Matt Wilcox has raised:
Change the design and those breakpoints are likely to be wrong. So you’ll need to change all of the client-side mark-up that references images.
I can give you a current use-case: right here on adactio.com, you can change the stylesheet …so I can’t embed breakpoints or sizes into my img elements because—quite rightly—there’s a separation between the structural HTML layer and the presentational CSS layer.