The basic ideas that can come up when writing a "shader demo":
Now, I chose 3rd option, that is, some non-realistic rendering.
Since the time of "Bzhykt" intro I was wondering whether it's possible to render the same entirely in hardware. "Bzhykt" intro is here (hey! don't run it! it doesn't work, crashes, and is a complete crap!). So, I set off for terrain, trees etc., with edges/hatches on it, and some "painterly" style. It's possible to achieve exactly the same look -- requires lots of rendertarget changes (similar to building a summed area table). But, alas, it didn't look good at all -- possibly due to some bugs on my part, possibly because of lack of precision or some other thing.
All in all, the final result is this.