For those who are still interested: I have updated the JS script, still available under the MIT License from my GitHub repo:
https://github.com/pettarin/rb_smil_emulator
Now it also works in iBooks for both iOS and OS X.
Note also that now Readium ships a complete support for Media Overlays (and a nearly complete UI/UX), so the default behavior of my JS script is to abort if Readium is detected.
Several (111 !) complete EPUB 3 Audio-eBooks, containing this JS, can be found here:
http://www.readbeyond.it/shortstories.html