I don't know, maybe the author is trying to do something with the iPad which is simply not supposed to do. The iPad is beautiful, pleasant to use etc. but writing a book on the iPad is maybe not the things one does.

I use my tablet to write — quite a lot — way slower than on my regular keyboard, but with time to think. Everything is in text files, synced to my desktop where the typesetting is really performed.

Writing publications or books is a long process where basically the final rendering is taken care at the end because the quality of the wording is more important.

So, just a text editor with hard work on the words, sentences, ideas are where 99% of the time is spent.

Maybe the author can provide an extremely pleasant way to write on the iPad and on the Mac with syncing of the work to have the feeling that the work is never lost, that one can always update a bit of the manuscript and just run "make" on the Mac some times to times. Everything in a smooth workflow.