[DaltonST]

https://www.edrlab.org/introduction-to-epub-4/

EPUB 4 will be a profile of PWP

EPUB 3 was created in 2011, but it didn’t replace EPUB 2 so far on most ebook distribution channels.

The WG charter states that EPUB 4 will be a profile of PWP, i.e. a specialization of PWP, with some additional features specific to the publishing industry (if any). EPUB 4 should be the ultimate interchange format for ebooks and other kinds of publications. It will keep most features of EPUB 3 (if not all), will make use of HTML5, CSS 3, javascript, media overlays, etc.

With some care and duplication of internal structures, it will be possible for a publisher to release EPUB files simultaneously compatible with versions 2, 3 and 4 of the format.

The modifications of such internal plumbing will not change much for publishers of simple ebooks and round-trip transformation between EPUB 3 (or EPUB 2) and EPUB 4 will be made available by the Readium community.

But EPUB 4 wouldn’t have a great interest for publishers and users if it was only a matter of plumbing. EDRLab will therefore push two innovations:

A solution for Web comics (and manga); an internal EDRLab Working Group has been created in June 2017 for preparing proposals to the W3C for such concept and structure; this will include page transitions and much more.
A solution for audio-books, currently never published using EPUB; an internal EDRLab Working Group has also been created in June 2017 on this subject.