2. with any integration, if there's enough demand, we'll do it. Once we add interactivity to diagrams, it should be trivial to emulate. However I should mention that Simon Brown (the creator of C4) has his own DSL for C4 https://github.com/structurizr/dsl)! We have no intention of competing with it.
3. Currently the options to tune are limited. The Terrastruct app has granular layout control via drag-and-drop, and we're working to bring some of that to native/open-source.
And there's C4 Model for Visualising Architecture [0] that has upcoming tool support, for instance Structurizr DSL [1]. It has an online editor [2] that can export to Mermaid, PlantUML and other formats. And has various open source repo's, like this Java codebase for the DSL itself [3].
[1] https://structurizr.com/help/dsl
The actual standard is quite light weight, which is its main selling point. The whole premise is that many teams find rigorous standards like UML and Archimate too heavy and thus resort to basic boxes-and-lines diagrams. C4 essentially says "take your boxes-and-lines and put full sentence descriptions on everything". Combine that will successive levels of detail, and you have the C4 standard.
You don't have to give up diagrams-as-code because you can create C4 diagrams with PlantUML [0] or using the C4 specific DSL [1].