We're using Python with Django. AppScale (similar project as TyphoonAE but a bit more mature) has done a decent job of writing a layer that implements all datas

We're using Python with Django. AppScale (similar project as TyphoonAE but a bit more mature) has done a decent job of writing a layer that implements all datastore functionality on top of variety of databases (some SQL, some not.) It's not too tricky actually since in most ways the App Engine datastore interface is a subset of SQL (kind if like SQL without joins actually.)