My employer, Grand Rapids Community College, is one of two schools taking part in a pilot program being offered by the Follett Corporation (the entity the college outsourced its bookstore services to several years ago) to rent textbooks to students as opposed to forcing students to buy them, which could result in a savings of over 40% in some cases.
It's likely Follett is being forced into this position by online services like Chegg.com which offer textbook rental and are quickly gaining popularity.
Given how much dissatisfaction there is out there with textbook prices, I'm amazed this didn't happen sooner (though the used textbook market and meta-search engines like BigWords.com have helped keep text prices lower). That same dissatisfaction could provide the momentum that gets the open source textbook movement going.
It's an uphill battle (as California is finding out), but if academics could agree on a universal platform upon which to develop them, open source textbooks could be the future. Think of it: a world where everyone has access to free textbooks created by the brightest minds from around the world on any given topic and proofed by thousands of pairs of eyes. If published on a flexible base (like XML), they could be turned into digital texts (or students could pay a third party to print a copy for them), they could be readily turned into versions for students with disabilities (braille or audio), pushed out to mobile devices, or incorporated into enterprise course management systems like Blackboard.
Interestingly enough I don't think traditional textbook publishers have to disappear in an open source model. They could sustain themselves by focusing on the ancillary textbook material for faculty: translation services, banks of test questions, suggested classroom activities, exercises, multimedia teaching aids, video game modules, etc. - the opportunities are limitless.