Based on the docs and the code within `pathlib2`, it seems to focus only on backporting the main features of `pathlib` to be available for Python 2. It does _not_ provide features in newer Python versions of `pathlib` (such as `is_mount`, new in Python 3.7). Therefore, it doesn't provide anything that the standard library of Python 3.6+ doesn't have. Differential Revision: https://phabricator.services.mozilla.com/D117071