In reply to Gary Jones.

TGM Plugin activation is just for making sure other plugins are installed and activated. It's a form of being able to include third-party code, and does use WP to handle it. However, it doesn't cover any third-party PHP packages the same way Composer does, or third-party JavaScript like npm or Bower does. So there is still a lot of work needed to be done to create a developer-friendly ecosystem that allows for third-party code.