Other obvious candidates for variable-pitching are basically any mode
that displays data in tabular form. And, of course, the manuals, but
that'll happen by itself once we move from .info to .html.
Is this a serious statement? Please don't do that. I can browse an entire Info manual easily inside Emacs nicely by pressing the spacebar and delete only. I can search entire manuals quickly and move across manuals easily.
Of course, it would be fine to additionally output html format for web viewing since the Texinfo/Makeinfo package already supports that.
Old fashioned sometimes is better. If only Scribe had survived, millions of hours would not have been lost in Word and LaTeX formatting and now the minimalist Markdown to get worse results.
-- Bob