First off, with the ongoing ebook revolution already in full swing, more and more people are turning to their mobile phones, tablet computers and dedicated ereaders to enjoy the works of their favorite authors. These are all devices that readily appeal to a teenage (and even preteen) demographic.
Secondly, having a literary juggernaut like the Harry Potter series in ebook format on webstores like Amazon and Barnes & Noble can only mean good things for all current and future writers of Middle Grade fiction (like yours truly).
Middle Grade fiction are books written for kids ages 8-12. Examples include the likes of Charlotte's Web, The Bridge of Terabithia, Nim's Island and of course the Harry Potter books. And of all the genres out there, Middle Grade has been the one with the lowest rate of ebook reader adoption, with romance being the obvious forerunner.
The reason for this is that unlike other genres, where the buyer is typically the reader, MG books are normally bought for kids by their parents. In other words, writers of such books must not only write books that appeal to their target audience, but their parents as well. A tall order if you ask me. So either of two things tend to happen at the end of the day. Either the book resonates with the parent (the buyer), but doesn't connect with the child (the reader), or the book offers precisely what the child (the reader) would like to read, but is deemed inappropriate by the parent (the buyer).
This problem is even more pronounced in the realm of ebooks and webstores than in traditional bookstores. The average parent wouldn't be willing to hand over their credit card to their twelve year old so that he or she may go shopping on Amazon. But they might probably hand them a few dollars so they could grab a copy of the latest Goosebumps or Animorphs (or whatever it is that kids read nowadays) from Walmart.
So what does any of this have to do with the Pottermore Shop you ask? Everthing! But most importantly, a whole new generation of kids would be getting their first taste of Harry Potter through Pottermore. And do you know the first thing they'd want to do once they realize just how wonderful the reading experience can be? The same thing we did all those years ago: pester their parents (or whoever) for more books of similar ilk.
All this could be wishful thinking on my part. But I really feel this is a good time to have an MG series in the pipeline. Only time would tell though.
P.S: I am an advocate of not judging a book by its cover, but boy do the new Harry Potter covers look fairly horrendous.