Re-implementing Lit from fundamentals is a great way to learn how it works! The core functionality is surprisingly simple, because it mostly relies on platform APIs to do the heavy lifting, like parsing templates.

I made this alternative implementation of lit-html to use as a research bed a long time ago when I was actively contributing to lit: https://github.com/ruphin/lite-html

Judging from this thread, many people have their own implementations, which is great to hear. I think there's a lot of value in solutions that are so simple that anyone can reproduce them.