> What I wanted to express was this: if you want to write _a book_, first write the book and only then worry about the tools. If you then notice that you need a custom toolchain to get the book in exactly the shape you need it to be, do it.

I agree 100% with this. Following the case of Knuth/TAoCP/TeX, in fact the first edition of TAoCP was not written in TeX, he made TeX to improve his already written book.