Just to clarify, I haven’t said that Webflow was working on that, but that we are hoping to see such feature in future. LASS/SASS was visible only as a text at the first version of playground (http://playground.webflow.com/) and at one of the images at the first version of Webflow.com website.
If you are looking forward for such feature, please make sure to post that in Feedback/Wishlist category (http://forum.webflow.com/t/about-the-wish-list-category/6516).