I am mainly unsure about if/how this should be turned on in Texinfo files.
Just make it an option, say, @microtype on|off. Off by default. (And forced to "off" when output is dvi.) That way it doesn't disturb anyone. I would not advocate for it to be on by default. This would lead to variant output between (dvi)-TeX, pdfTeX and possibly LuaTeX pdftex and luatex would normally have the same output. Any dvi engine, including xetex, would differ. which might be undesirable. In a theoretical way, maybe. But in practice, for most documents, the only TeX output that matters is pdf (i.e., not dvi). As I described in my original mail, microtype typically reduces the amount of manual rewriting necessary to avoid overfull boxes. Of course this won't be apparent just running on existing manuals, since the authors have already (hopefully) done all rewriting to get clean output, but for new and changed text, it can make a big difference in how much useless scutwork is required. I know it would help me a lot in the Texinfo manuals that I'm still maintaining. The main thing that would be useful beyond the patch is what I mentioned before -- it would be great to turn on microtype for \texttt, but then turn it off again for @example and @verbatim. But if you don't want to bother with it, the patch as it stands would be quite helpful. I find it hard to judge whether the output is an improvement. The aesthetic thing to look for (if you want to) is more even word spacing from line to line. There are some examples of the principle at the end of the memoriam for Zapf by Peter Karow (the first person to implement hz [not for TeX]). https://tug.org/TUGboat/tb36-2/tb113zapf-karow.pdf However, as I said, I don't advocate for this because of the aesthetics, but because of the practical benefit of reducing rewriting of text. The most notable change is that many less lines appear to be hyphenated. That's an improvement in itself. It's also an indication that TeX has more options for line breaking, i.e., it could use the hyphenations, so that the chances of overfull lines are reduced. is a lot of enthusiasm for this feature. Well, I have great enthusiasm for it :). So ... please? It seems harmless if it's off by default. We can hardly expect a groundswell of enthusiasm at this late date -- microtype is 30 years old and hardly anyone outside the TeX world knows it exists. Nevertheless, authors would appreciate Texinfo being able to avoid more overfull lines with less manual work. Thanks, Karl