This has long been in the works and now it's finally released: the Big Strategies Refactoring.
The most significant change in this release is the extraction of everything specific to concrete authentication/authorization mechanisms (e.g. the default OAuth 2.0 implementation) into strategy classes which significantly improves customizability and extensibility.
See the CHANGELOG and the updated README. There's also a blog post that introduces the release: http://log.simplabs.com/post/73940085063/ember-simpleauth-0-1-0.
I hope this is a significant step towards 1.0!