CSS2.1 became a W3C Recommendation on 7 June 2011. People have been using the HTML5 doctype for years now, never mind quite a few of the features. Arguing that the W3C is slow to standardise things is preaching to the choir, but CSS3 or HTML5 not being standards has had no impact on the ecosystem that's been using -moz-border-radius since Firefox 1.0. (that's 8 years ago. There are web designers that aren't twice that age out there).
Also, sorry to be that person, but isn't SASS/SCSS (edit: and calc()) "good enough"™. The problem with XML files not rendering nicely in the browser is not anywhere near as important to developers as XML not supporting a way of plugging in JavaScript as HTML does with <script>.
Edit: And lastly, what's wrong with XSL? It's got XPath, which as much as people love to dump on it, is not that bad. And you get HTML with all the bells and whistles as an output.