There is a new website, EPUBtest.org, designed to allow publishers and their suppliers to see how EPUB 3 is supported across various apps, devices, and reading systems.
There is a
grid on the site, that shows how the epub3 standard is supported on various devices.
So far, Readium Chrome Extension 2.12.4, has the most complete support for epub3. Kobo ios app has the 2nd most complete implementation. Both required and optional features are looked at.