Hello,
A few years ago, I redid most illustrations and included them in the docs as SVG files. The primary driver was switching from PNG to SVG to better accommodate hi-dpi displays. I also committed the source files. Unfortunately, they're in a proprietary format and cannot be reused without a Mac and an OmniGraffle licence.
(Before someone starts listing the arguments against proprietary formats — yes, I learnt them 15 years ago, and yes, I still chose OmniGraffle's UX over Inkscape's. : You're welcome to redo the diagrams with Inkscape and replace mine as long as the result doesn't look significantly worse.)
While not ideal, this got the job done. Diagrams look all right on all kind of devices.
To sum up:
- I think SVG should be the preferred format for illustrations in the docs
- I'm worried about ASCII art on small devices: line wrapping would be a problem
- whatever you want to make the diagram as long as it exports to SVG and looks reasonable
- commit the source file so someone has a chance to reuse them, regardless of their format
Best regards,