Okay, fair point about the third party apps. But even without them, it's not obvious to me that writing a Django-nonrel app from scratch is the worst option available.
I've worked with Django for 3 years, and in my opinion Django actually has a non-negligible learning curve. If you have to give up the benefits of the full-stack approach and of the Django ecosystem of pluggable apps, you might as well go with something simpler, such as Bottle or Flask, or choose a full-stack framework that officially supports GAE, such as web2py.