Great article, Allan!
It's true, people need to show their work, and they need to work towards having worked on a production system.
Work up the complexity ladder:
Something like that. Depends on the projects of course. Some open-source projects may be more complex than a production codebase.
Each of those rungs can be more complex than the rest, though.
Don't stick to tutorials and expect to be able to make the leap to a 10-year-old codebase. You can do it certainly, but having practice reading other peoples' code can help make it a more seamless transition.