$rcid parameter is currently unused but the problem with removing this is it's a breaking change and will break subclasses that override this method.
One way of doing this safely after thinking and exploring about this for a while is to use __call() method since PHP doesn't support method overloading natively.
Extensions currently overriding this method are: EntitySchema, WikiLambda, and examples and MobileFrontend calls the method and passes it a recent change ID argument.