The Jekyll code base would need major refactoring to allow for the lazy evaluation when using `serve` (and it would break some plugins) and likewise for the parallel builds because this is done with `fork` (as Ruby doesn’t have proper concurrency with threads due to the global interpreter lock).

So rather than try to refactor Jekyll, it would probably be a better strategy to use my re-implementation as the basis for a Jekyll 4.0, I’d say it’s 95% feature compatible with Jekyll and only about 2,500 lines of code.

While writing it, I did want to reach out to the Jekyll maintainers to talk about this option, but it wasn’t clear to me how to actually get in touch with them (e.g. no jekyll-dev mailing list that I could find), and I didn’t want to open an issue about this.