O'Reilly followed up on this recently: http://radar.oreilly.com/2011/07/epub3-enhanced-ebooks.html and noted that EPUB3 could "yield enhanced books" that will work on a variety of devices. Up until now, the iPad has been the only device that supports embedded media files.Bob Kasher: There are three key areas EPUB3 is focused around: language support, greater accessibility, and increased multimedia support. Language support will allow EPUB3 to save and search non-Roman scripts — such as Japanese, Chinese and Arabic — as font characters rather than JPEGs, as in current EPUB support. This will make a much broader range of literature available to current and future reading devices from base EPUB files. It will truly internationalize EPUB.EPUB3 will also be better at integrating the current DAISY accessibility standards, to help make reading devices of greater usefulness to visually impaired readers.EPUB3 will be much more adept at supporting multimedia capabilities for both HTML5-based devices and the coming generation of tablets supporting both Flash and HTML5. It is hoped that in doing so, EPUB3 will help develop an enhanced ebook standard that can be used across a variety of media and content.Other developments include enhanced metadata support for discoverability, better facilitation support for touchscreen devices, and support for MathML, which we hope will open up greater opportunities for textbook publishers. EPUB3 will be a quantum leap forward in capabilities for future device support, but still backward compatible with current devices on the market.
It keeps getting better and better!