I switch between golang's proportional font and Nirmala UI. They look really good on high dpi screens and are just generally attractive fonts. Indentation width is a drawback since space characters tend to be small. Code that uses two spaces for indentation is not nearly enough of an offset in my opinion. Four space indentation looks like two space for a monospace font, which is generally good enough. Also punctuation can be an issue as proportional fonts tend to have small, easy to miss punctuation.