What is J.K. Rowling planning? Return of Harry Potter franchise?

If you haven't heard yet, J.K. Rowling has opened up two teaser sites. The first is a YouTube with owls and a countdown clock located here. The second is a website, http://www.pottermore.com/. This is obviously directly related to the Harry Potter universe, so what is it that she will be announcing in six days? The YouTube simply says, "The owls are gathering... Find out why soon."

What exactly is Pottermore? Your guess is as good as mine. I and many others have some theories on it, but we will find out the truth in six days.

Will it be a prequel to the Harry Potter franchise featuring his young parents leading up to the night Harry got his scar? Could it be some books featuring stories during their time at Hogwarts that we never read, or some side stories with their classmates such as Luna Lovegood and Neville? It could be Harry Potter e-books, but I don't see why all this fuss would be made over e-books. Maybe the original books would be released as e-books with new bonus chapters?

Or it might not even be a new book, and it's probably not. Maybe it is going to be some sort of video game, like an MMO similar to the Marvel Universe Online which was eventually cancelled? I would think it would be more than just any old MMO game if JK Rowling is planning this big announcement. Anyone have any other guesses? Speculation is all over the place, but we'll find out what Pottermore is soon.