The rust blog post covers this. Subtree performance is terrible on larger repos and they didn’t land something that would fix it on medium sized ones. That’s why they went with a better maintained solution that scales.
Yeah I vibe coded https://github.com/sluongng/capyfun during a hackathon recently to add a generative transformation layer on top of the traditional imperative transformations.
It has since been merged into git proper:
https://manpages.debian.org/testing/git-man/git-subtree.1.en...
https://docs.github.com/en/get-started/using-git/about-git-s...