I'm still working on how to get the message across, but the idea is this:
We all know CSS. We all know HTML. Most of us agree that neither is powerful enough to build modern web apps, hence the explosion of CSS-preprocessors and templating engines.
If we're going to build tools to improve browser technologies like CSS and HTML, let's build them using another browser technology: JavaScript. Instead of adding incompatible extensions to CSS and HTML, let's first port them as-is to JavaScript syntax and then do the extending there, where at least the tools we build will interoperate.
Instead of learning increasingly arcane/proprietary/underpowered syntax for looping or doing arithmetic or writing functions, let's just use the tools we already have. Not to mention this gives us a streamlined development process and lower cognitive overhead for free.
Feedback welcome.