However, in the web world, ES6 modules have a huge (pardon the pun) advantage that's just being realized. Because of the static nature of ES6 imports, you can eliminate unused code when you package it all together. The newest Webpack versions and Rollup are both taking advantage of this, and it can result in huge savings in filesize.

For example, lodash is a large library with hundreds of methods, and a lot of the time people only use 3 or 4 imports from it. If you use an ES5 version, you'll get all of those functions in a compiled bundle no matter what. If you use an ES6 version with Webpack 2, all the methods you use will end up being the only ones that are actually included in the final code.