As a children's book author, I have been considering Apple's future options for iBooks and whether they would venture into the world of Windows or Android. After all, iTunes runs on Windows PC and Apple Music will be available on Android this Autumn, so why not iBooks on other non-Apple platforms?
But when I look closer at Apple's use of iBooks, I don't see this happening. Books is an interesting side-show for Apple and it fits nicely into content-consumption on the iPad and iPhone but it's not a core business. The iBooks Store arrived with the iPad, as Apple touted the virtues of books on the iPad for consumers and in education. But it is not central to Apple's business and so does not receive the attention that say the iTunes and Apple Music stores receive.
Anyone who has interacted with the iBooks team will also know that the number of people behind iBooks is relatively small. The changes in the iBooks Store over the years have been gradual but not revolutionary.
Instead, Apple see the iBooks app as an important piece inside iOS and OS X. The benefits of the iBooks app come as part of the operating system and the user experience on an iPad, iPhone or (recently) Mac, and launching a parallel experience for Windows and Android is not something Apple will do. iBooks is key to iOS/OS X, which in turn is part of the user experience on an Apple device. The message is- if you want to experience the iBooks app, buy an iPad, iPhone or Mac!
Adding iBooks to the Mac was a nice extra but it is a different experience to using it on an iPad and iPhone. iBooks is most at home on iOS and especially on the iPad, then possibly on an iPhone 6 Plus, with other platforms such as the Mac coming at the end. Putting it onto Windows or Android is a further step away from Apple's central aim here.
In the end, while I would like to see iBooks extended out beyond iOS and OS X, I can't see it happening. With my author hat on, it would be great to reach new audiences. But as a long-time Apple observer, it goes against Apple's aims for iBooks, which is to draw more people to buy the iPad and other hardware devices.
[Note- at time of publication, the iBooks Author page still has not been updated to show that iBooks Author books can be read on an iPhone: https://www.apple.com/ibooks-author/]