Forking HTML into a static language doesn't make sense

If it is so hard to layer a coherent and not laughably overcomplicated runtime on top of a document viewer in 20 years, then it follows that it probably wasn't such a good idea to begin with. Unless you're hellbent to freeride on the web's success, and ruining it in the process. At which point we're trying to solve an economic problem (someone else's) via a technical solution.

To get a sense how far of the mark browsers still are, you only have to look into the problem of rich text editing on browsers, which is a natural step up from pure text browsing, and something the first browser did already. Today, this is only barely possible thanks to a couple rich text editor projects who made heroic efforts to work out browser quirks (with contenteditable such that the browser's spellchecking can be leveraged, or alternatively using Canvas/WebGl, essentially developing a browser-in-browser).

In a situation where browser vendors struggle to keep up, adding additional tech such as WASM is the last thing you want to do. When and if WASM gets even basic language infrastructure such as gc, DOM or WebGl bindings, or anything even mildly interesting, then it'll immediately become another maintenance problem. And as you said yourself, at best WASM can help port apps over to a browser. It's however not clear what the purpose of that exercise should be when said apps run just fine outside the browser. I'd say if there were indeed so many apps waiting to be ported over to running in the browser, then there have been sufficiently sophisticated transpilers for like 15 years now (emscripten, gwt, many others), so I'm not buying that as an argument to make browsers even more complex.

Could it be a common language? Perhaps. I liked HTML2. I hated basically everything which went into HTML3 and HTML4. HTML5 has made a lot of good progress on rolling this back, but we're not there yet. It's possible to write parsable HTML5, but most organizations don't do it, and the ones which do don't have common ways to do it.

It's hard to remember, but back in the HTML2 days, the web had a certain type of client-side programmatic experimentation which is absent today. Anyone could write a tool which would grab things from the web and do meaningful things with them, and many people did. Google evolved from Altavista, which was a tech demo at DEC.

To be clear: The web is a lot more programmatic today in a general sense (client-side browser extensions, AJAX APIs, embedding webkit, etc. etc. etc.), but one part of that flexibility is gone, and it was important.

An SDO could say "we're doing project X", but if nobody shows up…