<canvas> is already a middle finger in the direction of accessibility. You don't need wasm to put blind people at an extra disadvantage. SVG Accessibility anyone? No? What a surprise. Classical web accessibility has basically ended. We (blind people) are only using sites which are sufficiently old to be still usable.
I'm genuinely trying to do something about <canvas> element accessibility. Whether it's enough ...? Probably not. But if I can do the work to try and show that <canvas> elements can be made more accessible, then there's no excuse for developers working on far more popular JS canvas libraries from making an attempt to better my efforts.
I do strongly agree that <canvas> elements should not be used to replace HTML/CSS! My personal web hierarchy is 1. HTML/CSS/images; 2. Add (accessibility-friendly) JS if some fancy interaction is useful; 3. More complex - try SVG/CSS; 4. use <canvas> only if nothing else meets the project requirements.
Well, I am not a web dev... At least, my know-how ends when SPAs begin. All I can point you to are the WCAG, but I am sure you already know about them...
Regarding the vague criticism you mention, I'd need something more concrete to tell you if the rumors are truish...
There has been some exploration around developing a JavaScript API for accessibility. If implemented, that would allow <canvas> renderers to be accessible. I hope people will consider that blocking for shipping canvas renderers, but we'll see.