Matt here, one of the folks working on Mobiledoc and the related editor. This blog post definitely served as early inspiration for our work. I dare to say we do a number of things better than medium now.

Mobiledc-kit is on npm as amd and es6. I believe also as CommonJS for browserify, but open an issue if it isn't.

If you use Ember, this add-on provides a more complete UI:

https://github.com/bustlelabs/ember-mobiledoc-editor