Requiring that a markup language (that must be sent across the wire between multiple buggy parser implementations) be hand editable is a recipe for disaster, and will never be as flexible as building/modifying an appropriate AST in a scripting language.

There's not even a good reason to read HTML anymore. You hit Ctrl+Shift+C in Firefox (or I think it's J in Chrome) and you view the actual machine-parsed DOM structure. The only reason human-editable/readable formats were ever necessary is a lack of appropriate dev tooling.