When widgets are SystemImmutable, as opposed to UserImmutable, this is because the system was consciously locked-down by a system administrator, in this case Kickoff should become essentially read-only, ie.:

• Favorites can no longer be added, removed, or re-arranged
• Applications can no longer be added as launchers to Task Manager (dunno about that, also needs similar adjustments in Task Manager)
• Applications can no longer be edited or hidden (the latter looks like a Kicker-only feature) or uninstalled
• The KMenuEdit shortcut is removed from the right-click menu

You can, however, still:

• Drag applications elsewhere to make eg. a desktop shortcut
• Access recent documents in the application context menu (does KActivitiesStats honor KAuthorized restrictions on recent docs and do we have that?) as well as jump list actions

Works nicely, requires https://git.reviewboard.kde.org/r/127909/ for plasma-framework

Inspired by the current discussion on the enterprise ml