For the future for epub4 see:
https://www.w3.org/TR/2018/WD-pwpub-20180104/
Please note epub4 breaks all backwards compatibility so it really just represents a packaged streamed set of web pages and apps
For epub3.2 or ePub 3.0.2 discussions:
https://docs.google.com/document/d/1...EY/mobilebasic
and
https://github.com/w3c/publ-epub-revision/issues/986