Symfony is awsome. Instead of hard-linking with twig templating system inside a framework. I propose to let user to choose which templating system to use. Ok, good to have something by default. I even tell that let's it will be twig. But, please, implement a clear way how to completely replace a twig with something another. Pure PHP, for example.
Let's say that I expect that framework should provide a clear interface to integrate any of templating system into it. It's enough.