When it comes to progress on the e-learning curve, one could easily argue that the music industry is well ahead of the book publishing industry. Napster and other illegal file-sharing tools forced the music industry to wake up and smell the coffee. Apple then stepped in with the iPod/iTunes combination and promptly ruled the world...for awhile...
As this BusinessWeek article notes, the pay-per-song model might be living on borrowed time. All you can eat subscription models like Rhapsody are gaining popularity. It makes sense to me. After all, I don't care how much music I "own"; I just care how much I have access to. Would I pay $12.99/month for the right to fill up a 30-, 40- or 80-gig MP3 player with all the music I could possibly want? You bet, especially since I'll know the door is always open to download even more as my interests and tastes change.
Now stop and think about how this applies to the book publishing world. Could you imagine a model where you pay $X/month for access to an unlimited number of books? It's never going to happen in the print world but I think this could be the killer app for the Kindle, a world where manufacturing and distribution costs are zero. Access to every single book in the entire Kindle library could be yours for a monthly fee. Assuming the monthly fee is reasonable this could be the model that really kick-starts the e-book industry.
How would publishers and authors get paid in this model? One option is to go by pageviews. Although the capability doesn't exist in Kindle 1.0, there's no reason version 2.0 couldn't be built to track pageviews of every book downloaded and read. At the end of the month the device could upload the customer's viewing history back to Amazon so that the monthly fee could be split among the publishers whose products were downloaded and read. Publishers would then pay authors their contractual share based on that same data.
Sound complicated? It's a model that's already in use today. Consider Books24x7, a great organization with a platform that "enables users to search, browse, read and collaborate with other users of these vast professional libraries." It's a very useful model and one that quite a few publishers are already participating in. A next logical step is to offer a library that's much, much larger and available on a device like the Kindle.
Would this mean the end of physical, printed books? Of course not, but it's a very interesting model that could be an excellent option for a lot of people (including quite a few who see no reason to buy a dedicated e-book device).