This article does not have any new news other than google and amazon are working with J K Rolling. The original Pottermore announcement said the Harry Potter ebooks would be available in all major ebooks formats.
I imagine it will be similar to the Baen ebooks store where you make your purchase and then select your preferred format.
I actually think it would have been better for Kindle users if they were just released them as .epub such that Amazon would have to consider supporting other formats. It will be curious to see what Overdrive does with Library/Kindle ebook loaning that is due to be announced soon.
I imagine it will be similar to the Baen ebooks store where you make your purchase and then select your preferred format.