All the methods and properties are now private in Enumerable - 4.6 - Ember API Documentation
Why?
This is just a guess but perhaps because most of that stuff will likely be superseded by actual future ECMAScript standards (ES7, etc) when they are finalized. And so the Ember framework wants to preserve flexibility by keeping it private.
Thanks for the feedback. I will restrain from using Ember.Enumerables until we have more information on the subject.
https://github.com/emberjs/ember.js/pull/11362
There has been PRs since to mark methods as public, so perhaps this may be one of those scenarios where it may or may not have been intentionally marked private.
Likely relevant, there is also an issue opened by @stefan to deprecate Enumerable: https://github.com/emberjs/ember.js/issues/11451