As feature freeze is rapidly approaching there is still a LOT to do in relation to converting the theme system to Twig. We will be sprinting to work on any Twig or theme engine related issues in the core issue queue. As the event draws closer we may a narrow down a set of tasks to work on. If you can create patches, test patches, review patches, improve documentation, please come out and help make the Drupal 8 theming system awesome!
See this url for more info - http://groups.drupal.org/node/289908