The "deployment scanner" is not available in domain mode. That is present only in the standalone mode of WildFly/JBoss.
Thats the reason inside your domain.xml file you won't find any subsystem with name "deployment-scanner", As that subsystem is only found & designed for standalone mode.
The deployment scanner is only used in standalone mode. Its job is to monitor a directory for new files and to deploy those files. It can be found in standalone.xml:
No, unfortunately that is still marked as Feature Request ([WFCORE-405] Filesystem deployment scanner for a managed domain - JBoss Issue Tracker) and not much progress happening on that. Until WildFly 10 CR3/4 i do not see any such feature introduced.