When the IDPF merged with the W3C a couple of years back they tried to develop a new standard called PWP, Portable Web Publications, which was supposed to be a new 4.0 version of EPUB, as far as i know. But there was much resistance from the publishing community and the project was shelved a couple of years ago.

See: https://w3c.github.io/dpub-pwp/publishing-snapshots/FPWD/Ove...