This led to a revelation that e-books (at least when read on wireless devices) feed the instant gratification we expect from the modern age. He took it a step farther and projected a future where wireless reading devices like Kindle interact better with the web and people write books that are meant to be read on them— books that allow the reader to link out to other documents, play music, and have more illustrations or even supporting data included. This prediction is probably relevant only (or at least mostly) for nonfiction. However, some of his other comments are on point. Shorter fiction is easier to sell in ebook form, one story at a time. It's true that the free sample feature on Kindle will encourage writers to make that first chapter a real grabber; new authors have to do that now, but even established authors may find that their readers want to try before they buy when the technology makes it so easy.
The one thing Johnson doesn't mention is the importance of e-ink. Netbooks are convenient, multipurpose devices that could easily be used to read books, but the screens are too hard on the eyes for long term reading. E-ink will have to master color in a cost-effective way before we get the shiny, be-all, do-all eReader than can surf the web and allow us to read Moby Dick in comfort.