Sounds like you didn't actually read the article, or understand what it said. Of course the OS is not for you. You're either not a programmer, or else you're not a programmer who's been exposed to some of the really cool ideas of the past like Smalltalk and its IDE, or LISP machines. Perhaps you would not think of anything to learn from them either.
From a programmer's point of view a shell/file explorer that's integrated the way TempleOS's is is way cool, even if it's not useful for normal users. Sure C is awkward as a shell expression language. But it's still a super cool idea (even if impractical for most computer use today).
No, his hypertext format is definitely not a reinvention of docx. Reread the article. It's more like a more flexible version of the old MS .doc format actually, which was just a serialization of in-memory OLE structures, which was part of why doc files have always been so hard to read since the OLE objects themselves were always changing as MS worked on Office.
Actually, as it presently stands, his OS is very secure indeed. It's literally impervious to remote exploits, and you'll never run any insecure software on it because odds are if you ran it its only his software or your own. Sure if it ever became network-oriented it would be a huge problem. That's not the point, though.
You're absolutely right that TempleOS will ever find its way into any sort of mainstream use, obviously. But that's not the point of the article. The point is that this is a monumental work for one person, and that there are some really cool ideas that maybe we could learn from. Such as the blurring of a text-mode shell (a la bash) and something more graphical. The idea of embedding diagrams and documentation hyperlinks in source code is genius (and automatic ones at that), as are his annotations for struct members. Having a living coding environment is also very good. I would guess that if an environment like Visual Studio implemented this (kind of like Quick Basic 4.5 had back in the day; it compiled on the fly), programming in C or C++ would be almost as fast as Python since you could test and tweak individual functions as you wrote them. They would become live and callable as soon as you syntactically completed them.
So I think you missed out on a few things that we really can learn from TempleOS. If TempleOS had a few more features and dropped the VGA-only interface, it could be a very fun learning platform for programming and system concepts. In fact I think TempleOS could itself be made into a standalone, self-contained application for teaching programming. Would be similar to Squeak or Logo. Limited in scope but a good teaching tool.