Honestly, we (my team) gave it up for the time being. So many changes to both backend and frontend was starting to be a time sink.
We’re continuing to use Active Model Serializer. Having no proper documentation at this point, makes it really hard to do the simple things. We’ll wait for the api to settle down and docs be written. Same goes for the transition to Ember 2.0.
Don’t know for JSON API, but have you looked at the EmbeddedRecordsMixin?