I'm going off of memory here but I think it's approximately correct. They were playing around with the idea for a while of creating "virtual trees" to handle accessibility and ultimately had to abandon it for privacy reasons because you would be able to imply that anyone who was using the virtual tree was differently abled and that was a whole can of worms that couldn't be resolved.
I believe the spec you link is a future proposal at the moment. And I trust a consortium of folks from a variety of browser vendors along with folks from other interests over a single product, when it comes to trying to figure out a better way to make things more accessible. And maybe Flutter can just use AOM in the future when it's available in browsers.
As of Feb, 2022:
> While still in draft form within the Web Incubator Community Group, the Accessibility Object Model (AOM) intends to incubate APIs that make it easier to express accessibility semantics and potentially allow read access to the computed accessibility tree.
I'm going off of memory here but I think it's approximately correct. They were playing around with the idea for a while of creating "virtual trees" to handle accessibility and ultimately had to abandon it for privacy reasons because you would be able to imply that anyone who was using the virtual tree was differently abled and that was a whole can of worms that couldn't be resolved.