It would be good to be able to support multiple app instances in a way
that provides an easy upgrade path - e.g. allow multiple app-id's in
app.yaml? Maybe thats got other problems associated with it, but it
is a common scenario when delivering SaaS that customers expect their
data to be partitioned away from other customers, and while in some
scenarios it might be god to be able to have each customer on a
different version of the application, it is more likely that we
upgrade all customers at once, and this is transparent to them - i.e.
one of the benefits of SaaS is you are always on the latest version of
the software. It would be possible t write an external script that
managed this deployment, but it would be good if GAE understood that
this was a common requirement and supported it. This issue
also highlights that we need a little more flexibility when deploying
customer apps - making the app-id unique obviously necessary - but
that shouldn't need to be exposed in the URL on custom domains.