I'm developer of Question bank improvements (https://moodle.org/plugins/browse.php?list=set&id=78) plugin set. After qbank refactoring in 4.0 i've lost ability to add plugins to navigation.
Previously i used <pluginname>_extend_navigation_course to extend navigation, but with default 4.0 theme this nav is not displayed anymore. qbank_action_menu::export_for_template has hardcoded values and does not respect plugin navigation nodes, declared by plugin_feature.php / navigation.php. This class should create menu items same way as question_extend_settings_navigation, or callback plugins in some other way.