I love bookstores, but I have never understood how they stay in business. What other business maintains an expensive inventory, most of which will never sell?
I suspect the future is digital, and printed books will eventually be one-offs, custom printed to order. This has already been tried, and I think it will eventually work.
Digital paper is already in the realm of possibility. We are within 50 years of a revolution in printing.
I would say closer to 15.
Don't discount audio books. Books that are mostly narrative and not overly technical lend themselves to this format. I always have one available when running, driving, or just tinkering around the house.