Good presentation, clear slides. Especially interesting thanks to the discussions that started during the presentation.
Maybe the code samples could be updated to use PHP7 (return types etc.). Would love to see more practical examples when it comes down to layering the application in combination with Symfony.
And as you stated at the start: quite a lot of information is useful for PHP development in general, not specific for Symfony. That's not a bad thing, but it might be a bit different from what people expect when going to a Symfony 3 talk?