I propose to introduce @Autowire annotation that will inject services into private / protected properties (the same way as Doctrine does with entities) instead of passing them to constructor. This can work like so:

class Service
{
    /**
     * @Autowire
     * @var Symfony\Component\Routing\RouterInterface
     */
    protected $router;
}

This would mimic Spring's @Autowired annotation and allow simpler DI if necessary, especially when inheriting services (on a small performance cost of reflection call, which is to be measured). Of course, container - injection should stay.

Was this behaviour discussed before?

See: http://www.baeldung.com/spring-autowire