Fear not, StealJS is here! Watch the video below, and checkout how you can get started using ES6 today, now, literally in the next 6mins (possibly sooner if you type faster than me - trust me you do).
StealJS can be built with a build step, but as the video above shows a build step is optional. StealJS handles module loading and ES6 transpiling all on the fly. All ES6 syntax supported by Traceur can be used with StealJS, in addition to importing and exporting modules.