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I cannot see a schema for this.
Putting all of these overrides in one config object could lead to large objects being sent to/from the database and cause issues later down the track. 
The methods on this interface tend to loading single items, why aren't we using single items? They could be config entities w/ a plugin bag to hold the plugin instance.
This looks like the drupal 8 equivalent of using variable_set/get to store massive blobs.