I don't think they're trolling - I have some similar feelings about this too. I think the main point is that outside of document-centric websites (say, Wikipedia), rich webapps are basically grossly abusing HTML to wrangle it into a semi-sane (but not really sane) way to render desktop-style UIs.
Think GMail, think Pandora - neither of which parses logically as a document, but are made from HTML: horribly hacky, horribly complex HTML at that.
It would seem to me that we're making HTML do something it was never meant to do, and that there are many applications on the web today that really don't need that stack at all, and really just need code and a renderer (like, say, a desktop OS).
Of course, this is a double edged sword. Simply tossing a renderer to devs is just going to invite a whole slew of confusing, non-standard UIs. Though, that said, if you look at GMail et al, we're already there.
"you do not want to render text or form controls in WebGL"
You don't. I don't. Our users don't. But trust me, there are plenty of ex-Flash devs out there positively ITCHING for a return to the days of un-navigable custom UI elements.
asm.js and WebGL give a hope that one day we will be able to forget most of HTML, CSS and JS like a horror dream they are. At the very least there should be a real choice of in-browser GUI technology and language (no crappy transpilation apart from asm.js please).
HTML and WebGL are mostly orthogonal. For example, you do not want to render text or form controls in WebGL.
We can improve HTML rendering with GPU-accelerated compositing, but that's mostly behind the scenes.