What will be the upgrade path to Python 3.x for Google App Engine Applications?
At least at the being, Guido was working closely with the team at Google who is building AppEngine. When this option does become available, you will have to edit your main XAML file.
I agree with Chris B. that Python 3.0 support may not be forthcoming too soon, but I'm not sure I agree that it will come sooner than Perl or PHP. At the Google I/O conference last year, they were very mum on what future languages they would support on AppEngine but they were pretty clear on the fact that they're actively exploring how to safely allow other code to run. One of the main reason they chose to support Python is that they due to it's dynamically compiled nature, they could support 3rd party library extensions with the minimal restriction that all add-ons must be in pure Python.
I wouldn't be surprised if Python 3.0 support was introduced sooner than new languages.
What is required to make the transition to Python 3.x for Google App Engine?
I know Google App Engine requires the use of at least Python 2.5.
Is it possible to use Python 3.0 already on Google App Engine?