Is it possible write a gulpfile in es6?

Yes, you can by using babel.

Make sure you've got the latest version of the gulp-cli.

npm install -g gulp-cli

Install babel as a dependency of the project.

npm install --save-dev babel

Rename gulpfile.js to gulpfile.babel.js

Your gulpfile might look something like this:

import gulp from 'gulp';

gulp.task('default', () => {
  // do something
});

Update for Babel 6.0+ As correctly pointed out by Eric Bronniman, there are a few extra steps involved in getting this to work with the latest version of babel. Here are those instructions:

Again, make sure you've got the latest version of gulp-cli
npm install -g gulp-cli

Then install gulp, babel core, and the es2015 presets
npm install --save-dev gulp babel-core babel-preset-es2015

Then, either add the following to a .babelrc file or to your package.json

"babel": {
  "presets": [
    "es2015"
  ]
}

Your gulpfile.js should be named gulpfile.babel.js

Note you can now use many/most ES6 features in Node.js v4.0.0 without babel. However apparently 'import' is still not supported. See: https://nodejs.org/en/docs/es6/

Edit: Most of the popular ES6 features (including destructuring and spread) are supported by default in NodeJS 5.0 (see above link.) The only major missing feature appears to be ES6 modules as far as I can tell.