Originally Posted by JSWolf
HTML5 is not yet standardized and has now been split off into two. So until HTML5 is standardized, ePub3 won't be able to be a standard.
Not necessarily, just as the current epub 2.0.1 standard does not support all xhtml elements, the new epub3 standard won't support all
HTML 5 elements.
I.e. the IDPF won't have to wait until the HTML 5 standard is finalized; they can cherry-pick the new features that they'd like to be supported by ereaders using the HTML 5 specs as guidelines.
Both Amazon and Apple already followed a similar approach.