While the Sony Reader Android app has had limited support for Epub3 since early 2013, their iOS app has lagged behind and was only updated this week. According to my source (and confirmed in iTunes), the new app only added support for the Epub3 fixed layout spec. This is going to enable readers to buy from a catalog of 20 thousand manga and magazine titles.
Sony has been pursuing their own ebook agenda for the past several years, and that includes opening several ebookstores in more markets (Australia and Germany, for example) and continuing to invest in developing their reading apps. But it does not include joining in the ereader arms race with Amazon, Kobo, and other companies; instead Sony has released basically the same ereader for 3 years running.