The dirty secret in all this is that e-ink readers, as currently designed, are going to have trouble supporting epub 3. Their microprocessors are not powerful enough, their display and lower power consumption is based on a static image, like a page of paper. Epub3 all but supposes a computer screen, a more powerful processor and probably net access. These are power drains which make the reader not so much like a paperback you can just pick up.
These characteristics are not going to be easily reconciled.
There are some people that read epubs on their phones. Popups that are great on larger screens may devour the majority of smaller screens...is this progress?
Again, hard to make everyone happy.
These conflicts will slow the adoption of EPUB3.