I am looking into using Google App Engine for a project and would like make sure I have a way to export all my data if I ever decide to leave GAE (or GAE shuts down).
Currently app engine datastore supports another option also. Data backup provision can be used to copy selected data into blob store or google cloud storage. This function is available under datastore admin area in app engine console. If required, the backed up data can then be downloaded from the blob viewer or cloud storage. For doing the backup for high replication datastore, it is recommended that datastore writes are disabled before taking the backup.