As I was reading this I felt that it overlapped and complemented the C4 approach in a lot of places. There's even a superficial connection: C4 is contained in the title!
Compare that to a C4 Landscape or Context diagram - and its just night and day - so much more meaningful information and the ability to express not just structure, but to provide hints at data flows, actors, and externalities. In the end, I've found the most value for C4 in communicating architecture to upper management and new hires. These diagrams really make more sense than boxes and lines.
For arc42 I find the document content really appealing - its like engineering thinking. There is no standard template/model for design docs, perhaps this could start a baseline or trend to do something similar. I do still prefer Structural and Behavioral classifications.
[1] Simon Brown, creator of C4 https://simonbrown.je/