I tend to think of interchange formats as human-readable and free of styling. SVG is definitely human-readable but it's harder to visualise than a well-formatte

I tend to think of interchange formats as human-readable and free of styling. SVG is definitely human-readable but it's harder to visualise than a well-formatted ASCII diagram, plus SVG marries content and style (text is styled by CSS, for example). The diagram aspect of an ASCII diagram is, I would say, structure, not styling, and so remains suitable for use as a basic interchange. SVG is great as an interchange for image editing, but I'm not sure that's necessarily what is best suited to basic diagramming. I'm sort of thinking like a diagram equivalent of Markdown.