I'm sure Harry is right, and this has been discussed extensively in other threads, but I haven't waded through all the other threads that started out discussing one topic and transitioned into discussing these issues. So, I appreciate the OP's question and link to an article that raises these issues specifically.
I think we will all have to wait until October to find out the answer to her question. If Amazon did start supporting ePub, even if just DRM-free ePub, that would be a pretty huge development, and I think you would have to give J.K. Rowling the credit for pushing Amazon into supporting the file format.
I'm just not so sure this is going to be what happens. It may be that Rowling just offers a Kindle (mobi or AZW) version of the books, but at least it looks like there is a chance Amazon will start supporting ePub.
P.S. I gave the original poster some karma. She has been contributing here for awhile, and although not a lot of posts, they are usually quality posts. I certainly recognize her avatar and am surprised she doesn't have more karma. Just say'n.