writing a device driver is easy. What's the problem?
Yes, writing driver is easy but imagine the instruction for running the demo -- before you run my demo, please copy this xdd to freemint's sysdir, reboot, run my demo and pray it doesn't kill your system. If so, I'm sorry for next reboot :)
Maybe this isn't such bad idea in general but I can't imagine how this could work for custom handlers, i.e. every demo/game coder would want to use his own specific code in VBL. And even when we find a way how to do it, we're back in the beginning -- such coder could write bad (leading to crash) code which will take whole kernel down and this is the current situation with Super()-ised democode.