Some time in the distant future, I see myself walking down the aisle of a bookstore. I see wikibooks for every subject. These wikibooks are not just any books, but high quality books in every level, high quality writing, high quality information, and high quality layout.
On wikibooks itself, there is a collaboration on every book. Not only are books worked on, but books reach a point where contributors can close the project happily, knowing that their book is so good, that it can get no better than its current form.
Realistically, I eventually see a company who will decide to capitalize on Wikibooks. This will alarm many people, but the company will realize that it needs to contribute towards Wikibooks just as much, and paid professionals will be able to hang out on Wikibooks, improving selected books, while the said companies sell quality books at discounted prices. The alarmed wikibookians will soon learn to take advantage of the situation, and after a period of "storming", both the company and wikibooks will live in harmony. (Similar to how Red Hat and Linux operate)