Through a circuitous Twitter path, I discovered this blog post from author Moriah Jovan. In it, she shows a sketch of her vision of the bookstore of the future: a coffee shop with ordering kiosks and instabook machines (called Espresso). Order the book and then it will be printed on demand while you sip your espresso. Astute readers already know that this magical machine is not fantasy. Several Espresso machines are already in operation in several libraries and universities throughout the world.
I think this could very well be one of the ways we are headed. Think how many problems it solves, such as the one we struggle with daily: whether to reprint a marginal-selling book or to let it die. Instead, we'd just make the PDF of the book available to Espresso and anyone who wanted it could just print themselves a copy. No more worries about getting stuck with too much stock or paying exorbitant unit costs on small print runs (granted, the unit cost is probably pretty high for an Espresso edition, but maybe the price to the consumer goes up as well).
The benefit to authors (longer availability of their books) would have to be weighed against the negative of maybe never being able to get their rights back from the publisher because the books would never be declared out of print.
I have a suspicion that Moriah isn't thinking about big reference titles and glossy, four-color coffee-table books. I don't think any quick-print machine is going to be able to match the quality and feel of a really nice offset-printed, heirloom-quality book. As long as we all recognize that going in, that's fine. Maybe the manufacture of those books will be left to specialists.
Of course, this is just one path our industry is likely to take. There's still the issue of e-books and which reader/format combo is going to emerge as the book version of the iPod. There will always be people who prefer their books printed (at least until we die off in about 40 years). But growing numbers of people will prefer getting their content electronically. So maybe eventually even the espresso/Espresso store will fade away as well.