I believe one of the biggest issues today is their choice of going with coffeescript - for everything ( including package development! ). If we want to involve the largest audience possible - then there is no doubt that - people have to go with javascript. They do support ES6 ( using babel ) - but as a pure javascript developer the documentation being in coffeescript means that - I have to go and translate coffeescript documentations to js and then understand how to actually use any particular api.
Having atleast a pure js documentation - would definitely help quite a lot.