With a DBus signal that is emitted when a file is received users can execute arbitrary actions. The share plugin already has an internal signal (https://invent.kde.org/kde/kdeconnect-kde/blob/master/plugins/share/shareplugin.h#L55). To export it to DBus it needs to be declared as Q_SCRIPTABLE.
To verify the behaviour you can use QDbusViewer
Check the org.kde.kdeconnect service under modules/kdeconnect/devices/<deviceid>/share org.kde.kdeconnect.device.share for the signal