That looks great! I wanted to do something similar and wrote a typst package called bookletic. I would love any feed back you have on how the process compares to what you have done. [bookletic – Typst Universe]
I think your package can be useful indeed for authors. It is nice to see the output straight away instead of my intermediate Python step. I guess you have also figured out in what way to order everything so that the pages are printed correctly? For me my Python script is useful because I sometimes like to create a book from PDF’s that I find on the internet like some books from the early 20th century or books that are out of print.
It insert blank pages if the signature is not a clean multiple of four.
I have thought about adding alternatives but a single sided variation would be the easiest to add.
I had never though about making books from preexisting pdfs. Right now the package takes in typst content blocks. That would be an interesting challenge to try and see if I could add that!