I wouldn't want to publish a book on Steemit unless I was 100% satisfied that it was a finished product.
The blockchain is forever, after all.
And as ready as A9 is for a publisher, it still would have to pass through a rigorous editing process before it could land on bookshelves.
While I'm not opposed to the idea of publishing a book on Steemit (TD may be a potential candidate), I will hold off, for now.