I agree with your main point about the binaries being small and a reasonable LaTeX distribution fitting in under 50 MiB (I think starting with a minimal MiKTeX and letting it install what you need a few times will leave you there as well), but regarding

> a manual source port to a different language is painful enough that nobody tried

there are in fact quite a few, many of which are complete: https://tex.stackexchange.com/questions/507846/are-there-any...