This has always been possible if you just write sufficiently obfuscated JavaScript. However a UI that is entirely rendered in a canvas element would basically be unusable by anyone with a disability, so that technique is useless for big orgs.
The cynic in me can't help but expect most web companies to care more about pushing unblockable ads down everyone's throats than about the disabled.
That’s why decent countries have regulation to make them care about things other than short-term profit.
It is not correct, but most big orgs don't care about those details unless they are legally enforced by the government.
I am yet to have worked in any web project where stuff like ARIA was even on the requirements list.
Unless they spent a _ton_ of effort re-implementing the DOM/native browser UI in canvas, it'd probably be basically unusable by anyone without a disability too.
What stopping anyone from adding accessibility features to single element canvas apps?
A UI framework developed exclusively for canvas-apps could probably add many such features.
It would also be impossible to inject ads into an existing wasm ui that didn't have them.
I thought the idea was to mostly use WebAssembly for parts that are performance critical, not replace all of it?