The intention of Hello-World is to check that compiler-linker and basic IO works.

A static blog generator checks that filesystem access works and your language provides a markdown and a template library.

Oh I mean it as a way to know how the language works.

EDIT for more information:

Being able to write a static blog generator means you have to learn most of the basic skills in a language from the data structures to objects/functions (whatever floats your boat). You have to also most likely interact with outside systems like I/O and databases (if your static blog generator is db driven). You get to familiarize yourself with packaging/modules that the language uses. So yea, I think creating a static blog generator as a next step after hello world would be great

I completely agree. I'm still working on my own but already i've learned a lot (among which, it's a bit more difficult than I expected.)

It does seem to make more sense to just roll your own static site generator rather than try to learn a whole new framework and language like Jekyll, which then might not even give you everything you want. This is particularly true if you where to use a robust templating engine like Jinja2.

For many it is - just take a look on GitHub for the massive number of static site generators people have written for various languages.