Awesome
sheetify-cssnext 
postcss-preset-env transform for sheetify. Use tomorrow's CSS syntax, today.
Installation
$ npm install sheetify-cssnext
Usage
const sheetify = require('sheetify/stream')
const path = require('path')
const opts = {
transform: [ [ 'sheetify-cssnext', { sourcemap: false } ] ],
basedir: __dirname
}
sheetify(path.join(__dirname, 'index.css'), opts)
.pipe(process.stdout)