Until full Query and QuerySet support is handled, and creating and using index tables for relationships dynamically behind the scenes, I wouldn't even begin to call this a backend.
Well, it's impossible to support absolutely everything of QuerySet. Also, it's likely that Django's official NoSQL support will be nothing more than what you get with this backend, so I'd say you can not actually call this a backend. :) In fact, this backend already provides more features than App Engine provides natively! So, you can actually get very far with it.
Indexing is planned for a later phase and we'll implement it in a way that is reusable between nonrel backends. In particular, this will be a separate optional module. The Django team probably will only support features that are the DB provides natively and that map to QuerySet (IOW, no map/reduce or other DB-specific features for which no SQL equivalent exists). By moving the indexing features into a separate module we can have the best of both worlds. Beginners don't get disturbed by automatically created indexes and advanced developers can achieve higher productivity because they can understand the automatically generated indexes.
