Much of the original needs solved by Knuth were needed by having Standard Pascal as the “assembly language” are not present in modern languages and as Github has demonstrated Markdown with friends can do a lot of work for documentation. Hence I thought, what can be done just by switching back and forth between the programming language and Markdown using comments and backticks carefully.
I had a rather complex but short Java demonstration program that I did this for at https://github.com/ravn/dagger2-hello-world (where the Java file is also symlinked to by README.md so Github will render it directly). I found Markdown to be expressive enough for my needs.
I am considering writing it up as a blog article.