HTML5 was explicitly designed for backward-compat with the large body of HTML4 (and earlier) content out there. And HTML5 can still be parsed using SGML, which as a superset of XML is every bit as powerful as XML, yet also has tag inference, attribute shortforms, and other minimization features dropped from the XML subset of SGML that are necessary for HTML, though. So there's no reason to be bitter about XML's demise on the web; I've even written a tutorial for XML workflows involving HTML integration or output using SGML [1].
[1]: http://sgmljs.net/docs/sgml-html-tutorial.html
> XML and attendant standards had also blossomed into fractal complexity.
Fully agree. It appears that once XML was out there, people wanted to apply it to each and everything. When markup is really only useful for semistructured text. In that department, you actually might find SGML much more useful, since not only can it deal with HTML, it can also parse markdown or other custom syntax (even JSON and s-exprs!), has built-in styling and transformation facilities capturing core CSS, and much more powerful templating and transclusion/fragment reuse mechanisms for actual text authoring and processing.