Interesting article, but I would rather go for http://www.projectoberon.com/.

Oberon is a really nice and very well documented programming language and operating system to experiment with. Unfortunately not that much distributions are still available (most links seem to be dead).

If you're interested in the OS or the language, here is a platform independent, stand-alone version running on LuaJIT: https://github.com/rochus-keller/OberonSystem

There is also an integrated IDE with syntax coloring, semantic navigation, and a source level debugger.

The compiler supports small-case keywords and underscores in identifiers. I'm currently working on an extended version of the language.