Amazon loves its subscription business models, so it's no surprise that the company might be testing an unlimited ebook plan.
The so-called "Kindle Unlimited" plan would reportedly cost $9.99 per month. It was first noticed by users on a Kindle forum, and then by GigaOM. Amazon has since wiped most the evidence from its site, but you can still see some of the test pages on Amazon's site and on Google Cache.
While Amazon already offers ebook rentals as part of Amazon Prime, users can only take out one book per month, and can only read those books on Amazon devices such as Kindle e-readers and Kindle Fire tablets. Kindle Unlimited would apparently be available on all devices--including iPads and Android tablets--and would have no reading limits.
Unfortunately, none of the major book publishers seem to be participating, as GigaOM points out. Though there are some smaller publishers on board, many of the titles come from Amazon's own publishing arm.
Still, some publishers are warming to the idea of ebook subscriptions, with Scribd and Oyster offering all-you-can-read books from HarperCollins and Simon & Schuster. If Amazon can offer a similar service that integrates with users' existing Kindle libraries, it could be a hit that shakes up the way people pay for ebooks. But maybe giving more power to Amazon is what publishers are worried about.