I'd say markdown is even better than HTML for writing generic documents since it enforces simplicity. In particular, it forces a linear flow of the document and does not have any support for stuff like JS.

And now many people are excited about throwing all of that away with canvas and web assembly.

Is it possible for developer to make canvas accessible? For example, pronounce "You are one the road that goes from left to right, there is a shop on your top and a inn on bottom" like mud.

Real accessibility is about presenting the same information your other users have. So, instead of you typing the description, let each of the drawn objects have its own description and made them discoverable and navigable. I think that Google were trying to make flutter2 components accessible, but it means starting from ground zero and building the same stuff anew.

right! But we would not need to use canvas if updating the DOM was not super slow.

I suspect the #1 reason is the layout/reflow engine but i might be wrong. Game engine do run physics at 60fps which is harder than CSS reflow.