The only people I've ever seen or heard of using proportional fonts for programming were utterly clueless freshmen newbs who mistook MS Word for a text editor...
Flash also come with a proportional font by default in the ActionScript
editor if I remember correctly. I believe
Adobe has changed its mind for other products with scripting support.
Caution: Stroustrup uses proportional fonts for snippets in the book
I use proportional Iosevka for most text editing, and just make exceptions per-language, e.g. for popular Ruby coding styles or Markdown tables.