A recent study from PIRA, a company that purports to be "the worldwide authority on the packaging, paper, and print industry supply chains" gives the future of epubs as they see it.
http://workflowprepress.com/262626/pira-releases-publishing-industry-technology-forecast.php
The e-reader market is likely to split into several distinct parts according to Pira, from the high-end color touchscreen with many other capabilities, through smartphones, down to cheap monochrome versions with simple controls to load and read titles. As the technology advances there will be cheaper, higher quality, lighter devices that will help reading and interactivity.
In a way we already see these separate markets from the black and white readers that are perfect for novels to the iPad which is more suited to full color apps, and can handle more complex files.
Through its well-publicized negotiated settlement with publishers and authors, Google can sell the full text of books, many of which are out of print. It is trying to broaden the content and is working with some 30,000 publishers to provide increased access, while creating new revenue streams for content creators, and Google. Over the next 10 years, it is in pole position to redefine publishing business models, while earning revenue from the sale and distribution of content.
When it comes to publishing the backlist in epus format Google and Apple are big players. Apple agreements require that a company post their entire backlist to Apple. Some companies just aren't ready to do this and are declining to sell books through Apple for the current year. I suspect it won't be long before they get on board though. However, the Google Books Settlement means that older backlist titles are going up anyway, and google will be profiting from there. Pretty big competition for any company who is getting into digitizing or distributing books.