I was blown away by the idea behind C4 when I first saw the presentation. I think what's missing is the tooling. I use C4 PlantUML do document my architecture designs.. what I'd really love though is a google maps style interface where I can zoom in or out of the current level I'm at. That'd be a game changer. Then you can really describe and understand the system.
The original presentation, in fact, used the google maps interface to illustrate the idea where you're first looking at a continent, then you zoom in to the city and finally the street level.
If you are using C4 right now, how do you compose the various level of architecture and navigate around them?
That’s because it’s flat
Imo this changes the game
Imagine being able to make a fully 3D graph inside a space the size of a large building
https://plantuml.com/
I'd say the big problem in visualizing big systems is that you can't usefully do it in one graph. For instance I worked on a system that had 2000+ database tables if you were going to make a diagram of that which shows everything it is going to take up a long wall. (This can be useful, but it is a big commitment)
A useful tool is going to let you make meaningful diagrams that show the subset of entities that are part of a story. I went to an art show of Mark Lombardi's works
https://en.wikipedia.org/wiki/Mark_Lombardi
who (before he was murdered) drew elaborate diagrams of conspiracies. One thing they showed was drafts that he made in the progress of creating his visualizations and he would sometimes make 40 or more of them. He would start out with a "hairball" that was disorganized and gradually figure out how to lay the diagram out in a way that made the meaning obvious.