Why Nim rather than e.g. Haskell (mentioned in the article) or OCaml, which are much more mature and have much bigger, more established tool/library ecosystems?
Because Nim syntax will be familiar to Python developer. Sometimes all you need to change is add variable declarations and rename `def` to `proc`.
Haskell has a much steeper learning curve. Been there, struggled with that. If I would recommend a functional language to Python developer, I would go with F#.