That was very in depth! As far as Pijul as a tool goes, I'm not seeing a git compatibility layer? So I think it's a neat project, but I probably won't try it because nearly all code is rooted squarely in git. Even if Pijul is perfect, you'd need to convince everyone else to use it.
Nevertheless, the increased interest in moving to patch based workflows from branch based ones is great. There's a lot of similar tools here (https://github.com/gitext-rs/git-stack/blob/main/docs/compar...) which I refer to infrequently.
Personally my favorite tool for living-with-the-reality-that-is-branches is git-machete (https://github.com/VirtusLab/git-machete).