Liza Daly just posted a copy of her presentation at Digital Book 2010 (last week). In this talk she discusses a number of Epub features you might see in the future.
A couple of thoughts
She mentions that none of the mainstream epub reader apps support these features. I would bet that calibre does. It's based on the Webkit browser, and Kovid never bothered to remove or limit its abilities.
I also find it somewhat interesting that the interactive features just now being considered for Epub look a lot like what you could do with Mobipocket 7 years ago. It's a shame that Amazon killed the format.