Made some mockups, showing the various colors, some KDE apps can include.
There are more to do, I know. But those are some of those widgets and decorations you can find around.
Oh jeez, I love it.
Investigation done: It's not
Qt developers apparently think it is not useful. It wasn't moved to QtGuiApplication, but is only available in QApplication (for QWidget-based apps).
Plasma/Wayland supports this, I've got a prototype plasmoid which allows to autorotate on X. Needs a bit more polishing and can be offered separately then.