What's missing from the old KCM is the application's icons in the comboboxes, since that's not supported by QtQuick ComboBoxes without using adding a custom delegate, however there's work on supporting it and the KCM does expose the icons to qml, so it's easy to add once supported.
What I'm not sure about is if the desktop files in the componentservices folder are necessary. Since I could not find how they are useful, I left them out for now.