I tried this, many years ago, but it did not take long before I gave it up. Code is full of skinny punctuation characters whose meaning is critical to understanding, and allowing a proportional font to squish down the screen area they occupy does not improve readability. This can easily be seen in the author's own screenshots.
Nope, no thanks.<p>Space indentation <i>after</i> text is very much a thing for me, and proportional fonts break that. Monospaced text looks neater to my eye, as well, and when I’m trying to figure out “how the hell that <i>ever</i> worked”, I don’t want the cognitive dissonance of trying to ignore the unaligned text.