That video shows a Drupal 7 site running within the Symfony framework.
This is an experimental fork primarily to demonstrate the low-level components of the Symfony framework and introduce them to Drupal developers who have not become familiar with Symfony yet.
It works, and I'm using it for real projects.
This project was briefly named Symfony Drupal.
I appreciate your thoughtful feedback on this documentation and the code. Please open an issue.