I was merely commenting on why HTML itself doesn't have the features you mentioned. But yeah, authoring HTML in SGML is the most natural thing given HTML's origins. It doesn't have to run as a static site generator since SGML can run right in the browser and in the web server backend (see eg my project here [1]). Though using SGML as static site generator from the command line or Makefiles is also extremely useful, and maybe the most appealing for developers or when static site hosting is desired ([2]).

[1]: http://sgmljs.net

[2]: http://sgmljs.net/docs/producing-html-tutorial/producing-htm...