From gulp 3.9.0, we can write gulpfile in ES6. But for this you need to add babel-core & babel-preset-es2015 plugin to your devDependencies and install it. Also You need to name the gulpfile as gulpfile.babel.js instead of gulpfile.js.

{
  "name": "some-project",
  "devDependencies": {
    "babel-core": "^6.0.0",
    "babel-preset-es2015": "^6.0.14",
    "gulp": "^3.9.0"
  }
}

Create a .babelrc file and add es2015 preset.

{
  "presets": ["es2015"]
}

I have explined in details on how to setup babel.js in my previous blog post.

Once you are done setup babel.js and presets you can write gulpfile.babel.js in ES6.

// gulpfile.babel.js
import gulp from 'gulp';
import browserify from 'browserify';
import fs from 'fs';

gulp.task('build', () => {
  browserify('./index.jsx')
    .transform('babelify', {presets: ["es2015", "react", "stage-0"]})
    .bundle()
    .pipe(fs.createWriteStream('./dist/index.js'))
    ;
});

You can use all the ES6 features in babel-preset-es2015.