Excellent thinking. Students would not be able to buy used books. Each student would have to buy a new electronic version. When you say "the next year students must buy their own," I hope you are referring to the next generation of students. For the students that just finished a class, the E-book should never expire; it should be theirs to keep. This has an added plus in that instead of students reselling their books back and no longer having access to the knowledge, students will now keep the books to look back at for reference. One cool thing about this is that if a professor in a senior level class asks if anyone has or remembers a certain fact from the sophomore level textbook, students will be able to look up the info right then and there, and when they graduate they will have their entire collection of textbooks (and highlighting and notes!) with them all the time. Hopefully, this will help boost productivity. If E-books can prove themselves to be reliable, dependable, and "life long DRM ownership," then E-books can be a huge boost to society.
One huge problem that needs to be solved: Right now, Amazon has the ability to "remote wipe" a book if they want to. This functionality needs to be ruled illegal. Once someone buys a book, it should be regarded as their [physical] property (just like a paper book). Right now there is a court case in Federal Court in which and AP student is suing Amazon for remote wiping a book, notes, and a book report that he had read and written ... just days before it was due. He went to work on his book report one day and it was gone!
http://www.minyanville.com/articles//7/31/2009/index/a/23821