Still in the early stages of design/development. However, here is an early, working prototype, implemented in WebKit as described here: http://www.xanthir.com/blog/ under "aspect-ratio CSS property".
Created attachment 70894 [details] Experimental Patch For aspect-ratio property
Stable permalink for the spec: http://www.xanthir.com/blog/b4810
Created attachment 75503 [details] Experimental patch rev. 2 for aspect-ratio property
FWIW, this has already been discussed at www-style http://lists.w3.org/Archives/Public/www-style/2010Oct/0046.html and http://lists.w3.org/Archives/Public/www-style/2011Oct/0550.html. It's just blocked on Tab and Fantasai having enough time to put in into a formal spec as far as I can tell. I don't see any problems with moving forward with this as a webkit-prefixed property.
I'll use this master bug to track the new aspect-ratio work: https://lists.webkit.org/pipermail/webkit-dev/2020-October/031543.html
<rdar://problem/75435850>
does it make sense for this to still be open? the one dependency is a much broader issue than just aspect-ratio
(In reply to Sam Sneddon [:gsnedders] from comment #7) > does it make sense for this to still be open? the one dependency is a much > broader issue than just aspect-ratio I would like to fix bug 222357 before closing this bug.