Of late I've been modernizing ExTeX[0] for integration with my markdown editor Scrivenvar[1][2] so that the editor can include TeX. My Typesetting Markdown series[3] dives into numerous reasons why I prefer to embed plain TeX in Markdown over LaTeX (skip ahead to parts 7 and 8). The text editor's TeX integration hasn't started yet[4], but if you're keen, star the GitHub page.

[0]: https://github.com/DaveJarvis/extex

[1]: https://github.com/DaveJarvis/scrivenvar/

[2]: https://www.youtube.com/watch?v=u_dFd6UhdV8

[3]: https://dave.autonoma.ca/blog/

[4]: https://github.com/DaveJarvis/scrivenvar/issues/69