Maxime Bernard's blog

It’s been rumors last February when they started to talk about building Drupal 8 with Symfony framework !

This is now confirmed on Drupal website. 

Based on the research and discussion here, we are going to integrate the Symfony2 HttpFoundation library. That is, we’re going to just bundle it with core, along with the Symfony2 autoload routines to make the code available. In practice it will almost always be accessed via the Context object, but that’s for a later patch.

But there’s still a license matter to resolve:

We need to work out the legal details, as Symfony2 is MIT licensed, not GPL.

We can easily imagine that Drupal will move progressively on 100% Symfony framework. 

By the way, the plugin named ”Sympal” (Drupal-like plugin on Symfony) should not longer be supported by the Symfony community.