I'm not sure how you guys see this as SAVING the Sony eReaders. Here's what an article on The BookSeller.com states:
The e-books will be released in October, and will be available only on the Pottermore website, but will be compatible across a range of devices, including Amazon's Kindle. The facility is being provided by the e-book vendor OverDrive, which also serves the Waterstone's and W H Smith's e-book stores, as well as being a major player in the library e-book lending market.
Complete article here
I don't see how this remotely affects Sony eReaders any more than Kindles and Nooks and all the rest. I too desire to see the Sony line of eReaders continue, but I think you are pulling at straw to read anything into this announcement other than the fact that Rawlings is trying to make even more money from her Harry Potter Empire. She obviously, and smartly, wants to control the sales and distribution of her eBooks and avoid as much distribution costs as possible.