Unix seems hard to learn because it started as a tool for experts, people who already understood the underlying concepts and had experience with other operating systems. Someone coming at Unix without some understanding of the fundamentals will struggle with it.

Unix doesn't refer (anymore) to a single operating system or collection of tools. You probably mean Linux, which comes in many flavors (distributions), or maybe to MacOS. No one company or organization makes Unix, and while the fundamentals and basic concepts hold across the Unix-derived operating systems the details -- things like command line arguments and directory structure -- can vary a great deal.

You conflate the core operating system with "user space" tools such as awk and sed, abstractions such as regular expressions, and vendor-specific things such as package management. We can lump those together and call them "Unix" but only in the same way we can refer to a generic "car" as a thing with an engine and four wheels.

I have taught several people how to use Unix/Linux/MacOS to some degree, to accomplish some specific tasks. I have seen them struggle with basic concepts such as directories and file organization, permissions, the whole idea of executable scripts, "piping" and redirecting input and output ("everything is a file" doesn't mean much to most people). When it comes to processes, networking, inter-process communication, different kinds of text files (ASCII vs. Unixcode/UTF-8, for example), etc. most people just get lost or lose interest because they don't have any mental categories or real-world analogies to connect to. Anyone approaching the problem of "learning Unix" today probably has experience using computers, but they really have experience using graphical user interfaces that hide the details and application programs such as Word or GMail that offer task-oriented user interfaces with none of the underlying fundamentals exposed. Learning the concepts that underly Unix, or any operating system, requires going down some rabbit holes to understand things like text file, directories, processes, and so on. Few people will have the patience and motivation to do that work, to read technical books on operating system fundamentals and design.

If I showed someone how to use grep to search text files for a string they might get that after a while, but they probably don't really understand text files or regular expressions -- they have just memorized the steps to complete a specific task. If I then tried to explain how to search a CSV or XML file that new information might not connect, and the person has simply learned how to do two or three very specific tasks without gaining much fundamental expertise. That's like someone memorizing a few recipes from a cookbook but not actually learning much about ingredients or cooking.

What you propose seems like trying to learn top-down, by practicing specific tasks such as text processing (largely incidental to the operating system). Some people can learn that way -- working through enough tasks with repetition will let them deduce the abstractions and encourage them to explore on their own. Most people will fail because years of schooling have discouraged that kind of thinking, making them goal-oriented and focused on completing a specific task by memorizing specific steps rather than actually learning. And many people don't have the motivation and desire to learn how regular expressions work, or what a "process" means in the context of Unix.

No amount of instructional design will help everyone learn a complex topic. Analogously, you can't get through medical school by practicing a few procedures over and over. You have to learn some biology and anatomy so the many things you have to study and remember make sense and hang together.

There's no way I know of to even have this discussion without coming across as as elitist. I learned Unix (and C) from the Bell Labs Technical Journal articles published back in the '70s because I had an obsessive desire to do that, and the spare time and energy of a teenage boy bored with high school. I put a lot of time in, sought out mentors, practiced, explored, studied. Everyone I know who has mastered a complex skill or set of tools tells the same story. My experience was more like learning a language by immersion than with flashcards presented in an app. I don't think most people incapable of learning Unix or any other technical skill, but I do think few people have the motivation, time, and persistence to do it, and instead want some easy way to get information spoon-fed to them, a process they already understand as "learning" because schools mostly work that way.

Good luck with your project.