I must say slowly base Gutenberg (without many plugins) is coming together and the vision that eluded me for so long is forming in front of my minds eye. Basically it offers a simple interface to newcomers or clients and all those tweaking are done through theme.json and and the HTML templates.
Only thing missing would be flexible interface (maybe as a plug-in) to edit theme.json… maybe a tree viewer with some mappings and auto detections for the best interface component. That would be a nice No-Code replacement for the customizer without giving up on the flexibility and open structure of theme.json while still offering an interface to the No-Code tweakers.