I don't get it. If you are using less or sass anyway.... why would you use myth as a post-processor, since myth doesn't do anything you couldn't do already in sass or less?

Considering what it does duplicates a small part of what less and sass do, why would you use it?

I used to be a big supporter of Sass, but now I prefer the simplicity of CSS. Look at almost any Sass project and it's usually overly complicated. I stopped writing Sass a few months ago and I haven't felt crippled at all.

The complexity of Sass/Less is starting to out-weigh the benefit of their features, for me at least.

That's on the individual project maintainer, though. Any valid CSS3 file is also a valid SCSS file, so you can add enhancements on top of that exactly as much as you want to.

var works differently in CSS than preprocessors, and in such a way that you can't combine them with preprocessed calc etc. statements.

Having said that, I don't know if this polyfills the var spec exactly.