You'll notice that I've loaded these libraries in addition to the latest version of Leaflet:
The implementation was not that complex once I got all of the numbers right. First I create a new Proj4Leaflet coordinate reference system which I pass into the map constructor. Then I use the Esri-Leaflet Plugin to set up a new TiledMapLayer and add it to the map.
Now you can be one of the cool kids too!