Here's my notional take on a unification plan;

Move the GAE/GCD detection logic from gcloud.datastore._implicit_environ into gcloud._helpers (#741: hoist GAE/GCD detection into gcloud._helpers #747).
Move the "project detection" logic from gcloud.storage._implicit_environ into gcloud._helpers (#741: hoist project detection/setup into 'gcloud._helpers'. #748).
Consider how 'project' and 'dataset_id' should be related (e.g., does an app running on AppEngine / GCE use the same logic to determine its project ID for storage / pubsub purposes?).
Add gcloud._helpers.get_scoped_connection(), which takes the connection class and a scopes list as arguments; make each gcloud.*._implicit_environ.get_connection delegate to that helper (e.g., via functools.partial) (#741: hoist get_scoped_connection into connection #749 leaves to original get_connection() functions in place, but has them delegate to get_scoped_connection()).
~~Move the _DefaultsContainer up into gcloud._helpers, and make it generic; instantiate it (subclassing only if really necessary) in each gcloud.*._implicit_environ.~~

Unify '_implicit_environ' handling #741

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