The ruby version is on feature freeze until libsass catches up.

Flenser · on Sept 1, 2015

citation now I'm on desktop:

> In fact, Ruby Sass will not release any new features until LibSass catches up. Once it does, there will be feature parity between the two moving forward. Soon, we’ll have the blazing speed of LibSass with all the features of Ruby Sass!

http://sassbreak.com/ruby-sass-libsass-differences/