In reply to Ryan Hellyer.

What is relevant, is that it is now much more straightforward to rebuild the admin interface

citation needed

wordpress.org sites can and do change their admin. doing it in php is not harder than in JS. The calypso relies right now on the limited set of interfaces provided by wordpress.com, but what happens when you use plugins to extend the functionality? You most likely need to release a new version of the app otherwise you have done nothing more then embedding the wordpress admin in an app.