New features are always good to have in JDeveloper - but missing new features, this is something really new :-) It looks like documentation is released faster than actual functionality. If you read What's New in This Guide in Release 18.104.22.168.0
document, it provides new documentation section about how to setup security for ADF Methods (see Chapter 35). There are nice step by step instructions available in Chapter 35, how to enable security for ADF Methods. This guide says you need to have command component to execute ADF Method, also ADF Security must be enabled. Finally documentation says - "The Resource Grants page of the overview editor displays all methods that your application defines."
. Well, may be I'm missing some magic check-box, but methods are not listed in the overview editor.