To maybe get this picked up fast:
https://tomhodgins.github.io/aspect-ratio-spec/aspect-ratio.html
You realize that's not an official spec but just someone with a cool idea, right?
yes. but sometimes putting things on here, or at least talking about it, speeds up the process of actual spec writing and implementation :)
On caniuse via MDN: https://caniuse.com/#feat=mdn-css_properties_aspect-ratio
In Chrome Canary 84.0.4145.0: https://twitter.com/Una/status/1260980901934137345
Most helpful comment
https://drafts.csswg.org/css-sizing-4/#ratios