We do have migration guides to the Flexible environment available per language. This is the link to the Python version: https://cloud.google.com/appengine/docs/flexible/python/migr...

I hope that helps. A key tenet in the Flexible environment is portability. In the Datastore case, in particular, if you move to Cloud Datastore, that gives you portability across the Cloud Platform offerings or even if you want to run on premises or in a different Cloud provider.