On my way to sleep one night, this window decoration popped into my sleepy head. Somehow I remembered to draw it in Inkscape the next day. This is not a working KDE window decoration and so, as I have no QT/KWin skills, I leave it up to y'all to be inspired enough to implement it - if you see the need.
Attached is the Inkscape SVG file containing the drawing. Please feel free to do pretty much whatever you want with it, so long as you always give proper credit as to where it came from ;)
*** UPDATE ***
Maxilys has gone through the trouble to actually implement this at the URL below.
Please take a minute to check it out and show your appreciation.