I regularly use TeXInfo, which is primarily a single macro file [0], which starts out as TeX, and has been completely changed into the new language by the end o

I regularly use TeXInfo, which is primarily a single macro file [0], which starts out as TeX, and has been completely changed into the new language by the end of the file (A new lang capable of conditionally embedding TeX, HTML, etc.) Being able to seamlessly transform the language on such a fundamental level is one of the reasons I don't think we'll ever see a next major TeX - all it would need to be is a macro atop of TeX. And then everyone has their own feelings, so it'd probably stay as is. [0] https://mirrors.kernel.org/gnu/texinfo/texinfo.tex https://mirrors.kernel.org/gnu/texinfo/texinfo.tex