While I truly agree that JS is one of the worst "scripting languages" in active use, (X)HTML and CSS are actually quite ingenious. Their only problems are legacy baggage and limited interoperability.
If I sat down today to build a technology for doing cross platform app development I would likely come up with some XML-ish declarative GUI customizable using something CSS-ish. In (X)HTML, almost all elements in the body are interchangeable, they just come with different default style sheets, and while I would certainly have defined a different set of elements with different default style sheets compared to (X)HTML, the principle would be the same. And I would of course use a different scripting language, probably Lua and/or Scheme, possibly Java (as scripts, using BeanShell, not as compiled jars).