Most useful features in CoffeeScript have been co-opted by ES6 and its proliferation will put pressure on CS to innovate some new features or become much less relevant. The "ideal" JS code near the end of the article almost is valid ES6. The following is valid ES6:

    var leftPartial = (fn, ...args) => function(...remainingArgs){
      return fn.apply(this, args.concat(remainingArgs));
    };
    

Run it in http://benvie.github.com/continuum.