I haven't worked with Ember's templating syntax, so don't have any thoughts to offer there. I was however bitten by Angular v1's templating, on which my comments were based.

SASS and LESS both add language semantics over CSS and suffer from the same problem. So does for example Jekyll's templating language. But in case of CSS, the language additions are a practical necessity - it lacks even basic abstractions, which the pre-processors provide.

So there - trade-offs.

I've written in more detail about this topic at http://www.jasimabasheer.com/posts/evolution-of-view-templat..., if you are interested.