Looking up the roadmap at Google App Engine, i see the following entries:
* Service for storing and serving large files
* Datastore import and export utility for large datasets
* Billing: developers can pay for more resource usage
* Support for a new runtime language
* Uptime monitoring site
As anyone can guess, Google would like to be secretive about the entry 4 above - Support for a new runtime language . But, come on, if you really going to release the new language, what is the harm in telling it right now. In my PoV, since it is going to be a major launch, better make developers prepared for it. If the new lang is going to be php, i for one, would put on hold few projects to make use of the Google App Engine. Anyway, as it seems, we would just have to wait for the launch.