No one's going to use WebGL as an alternative to the DOM until it supports accessibility (read: being visible to googlebot)
Even if it did, you'd still lose a lot of productivity with it if you're used to working with the high level of abstraction of the DOM, e.g. line wrapping.
There are certainly cases where dropping to GLSL is the only way to get a UI to work at all, but most of the time the metadata-providing feature of HTML is far more important than squeezing some milliseconds of performance.
Flash had better accessibility support than WebGL does today. Google could even crawl Flash content to a certain extent.
Besides, I said _WebGL as an alternative to the DOM_. Of course a complex visualization that can't be properly described with text will not care about supporting jaws (even though it might have gotten some free accessibility out of the box with Flash). If you rely on the DOM like most people do, there's a huge chance that you care about your text being machine-readable. Accessibility is just one of the showstoppers for generalized WebGL adoption. SEO is another.
I think some people severely underestimate the barrier of entry that WebGL/wasm needs to overcome to displace Javascript/DOM as general purpose tools.
Even if it did, you'd still lose a lot of productivity with it if you're used to working with the high level of abstraction of the DOM, e.g. line wrapping.
There are certainly cases where dropping to GLSL is the only way to get a UI to work at all, but most of the time the metadata-providing feature of HTML is far more important than squeezing some milliseconds of performance.