BSON ownership has been an issue when trying to use extension stages inside subpipelines, as the extension stages use 'getOriginalBson()' but during parsing the parent stage might not save a reference to the temporary BSON. 

Similar to the 'Matcher' class, we want to create a class e.g. 'OwnedLiteParsedPipeline' that preserves the lifetime of the BSON properly.