PGAE, 2nd ed. is currently in the "production" part of the process. I'm tidying up language and testing code samples, and O'Reilly has a copy editor working through the book. Then we do layout, indexing, and illustration. Naturally, all of these improvements will make it into the digital Early Release edition. I'm expecting a street date of late September or early October. I'm still working on the downloadable code samples as well.
Meanwhile, I'm preparing another O'Reilly webcast, currently scheduled for October 9, entitled Data Modeling for Google App Engine using Python and ndb. The 2nd edition doesn't have any material on ndb, but it's a compelling enough topic that hopefully this can serve as a brief addendum for now. I'm especially excited about this one because we will be broadcasting live using Google+ Hangouts On Air. This means we'll have a quality video stream, as well as an automatic YouTube archive available within a couple of hours after the event finishes. This is a first for O'Reilly webcasts, so bare with us while we work out the details.
If you're an Early Release purchaser and have enjoyed the 2nd edition so far, you're invited to write a review for O'Reilly's website. It'll be nice to have some thoughtful and thorough reviews on the site for the launch date. :)