GAE Blobstore file-like API deprecation timeline (py 2.7 runtime)
Official response from Chris Ramsdale, Product Manager, Google App Engine:

while there's currently no defined date for decommissioning this API, we are committed to supporting it throughout the remainder of the year (2013).  please don't hesitate to reach out to me directly [redacted], if you have further questions (this thread is fine as well).
This is a question for the App Engine team.
Last week we realized that the App Engine team had marked the file-like API for writing and reading to the blobstore as being deprecated and likely to be removed in the future. We have quite a bit of infrastructure relying on that API that now we need to port to the alternative they suggest (Google Cloud Storage) and this is not a trivial effort (especially considering our current backlog). So the question is: how soon will this file-like API be unavailable? It's fairly important for us to know as depending on the answer, we might shuffle our backlog to prioritize the porting of using the Blobstore to GCS. 
Thanks.