Tinkering and experimentation.

Could be a good use for older hardware. Why not.

How would unoptimized slop code be good for older hardware? That's what Linux and other projects are for. If you wanted to tinker and learn how operating systems work, you'd code one yourself like I did in CS classes. You'd actually learn something and you get the good feeling of having done it yourself.

You won't understand a thing, though. You already have the source code for Linux, Minix and tons of other OSes, pedagogical or otherwise. Why generate yet another that you won't understand?