Well, as I have Kobo ereaders, it will work well for me
But, it was really a comment on Jon's "no support". I named two ereaders, and they have a third, that already support epub3. So, Jon's statement is wrong. If he had said "little support", I wouldn't have commented.
Having said that, if it was my job to create an ebook right now, I wouldn't use epub3. Unless I really needed the function. Or someone was paying me to do it that way.