The menu additions have been checked on Linux and Mac OS X with Qt 5.6.0 - 5.8.0 and frameworks 5.22.0 - 5.32.0; the colour scheme addition with Qt 5.8.0 and frameworks 5.32.0 .
I looked for an appropriate way to uncheck the Tile/Cascade/Tabbed menu items (= when the user moves or resizes one of the MDI windows) but it seems those events are not available through signals and would thus require subclassing MdiSubWindow .
It would make sense IMHO to separate this demo from Oxygen. It has nothing Oxygen-specific and could be provided as a standalone theme explorer or bundled with another package that doesn't have too strong connotations of being "Plasma-exclusive" (Qt has widget style and palette support on most if not all platforms it runs on).