People will try all kinds of sketchy rigs to get their handlebars higher. With quill stems they could raise it way above the maximum height line. Supposedly that increases the risk that the stem might bend or break or that the steerer tube of the fork could crack because the stem no longer reinforced it at the end of the threaded part. Sure, it's possible, but has anyone ever seen it happen? I haven't. I don't advise raising the stem to ridiculous heights. I'm just saying that people who do it seem to avoid any negative consequences.
With threadless headsets, the home hobbyist has to get more creative. We've all seen the bikes with the bar ends sticking straight up. That was the 1990s version of the ten-speed with the drop bars turned upside down.
The owner of this bike assembled his custom handlebar out of PVC. It isn't even fastened together securely. If the rider hits a bump while leaning on that top section it will quickly become the bottom section. If the rider even leans heavily on it, it will move.
This setup takes its place alongside the sheet-metal home-built pant guard a man made for himself, which was basically just a meat-slicer blade going around next to his ankle, and the home-made chopper fork a kid welded and installed on his bike without a headset at all.