BigPipe and the Symfony Framework
The Drupal 8 development team is doing great improvements to the product regarding HTTP caching. With validation tags, contexts and so on it feels familiar to people working with Symfony2 framework and the FOSHttpCacheBundle.
Another interesting addition is an adaptation of Facebook's BigPipe rendering strategy, which downloads HTML snippets in parallel for improved load times. Symfony2 as a HMVC framework can load bits asynchronously, but there is room to improve.