David Sim posted an interesting piece in The Atlantic a while back about J. K. Rowling’s tendency to add little snippets of detail about the Harry Potter universe in unlikely places.
Of course, everyone remembers when she declared that Dumbledore was gay during an interview following the publication of The Deathly Hallows. But Potter fans know that there are lots of other places to look for tidbits of “extended universe” material. Rowling’s Twitter feed is one such venue. The Pottermore fan site is another. And of course, the Universal Studios Harry Potter theme park is like a life-sized Mary Sue fan fiction generator where guests can be chosen by a wizarding wand of their own (which they can then use in special spot around the park to cast their own spells and cantrips).
More formal additions could be on the horizon, considering how much interest Rowling still has in the world she created, but hopefully said works can stand on their own, rather than plugging into a fan-service feedback loop. The more Rowling enhances and embellishes her Harry Potter universe, the less room she leaves for readers to fill in the gaps with their own imaginations.
But my experience with fan culture actually leads me to think that the opposite is true. All of these cross-platform “embellishments” suggest that the Harry Potter universe is alive and constantly evolving. Rowling is famously supportive of fan fiction writers (unlike George Lucas, to whom Sim compares her in his article), and to me these tweets and updates read like an invitation to readers to write. Each new detail, such as which house Harry’s son James S. Potter was placed into by the Sorting Hat or the reveal of an American school of magic with ties to Native American culture functions more like a prompt, a story idea that Rowling is inviting fans to flesh out. Rowling’s forthcoming projects set in the Harry Potter universe (the forthcoming movie, scripted by Rowling herself, called Fantastic Beasts and Where to Find Them and the stage play Harry Potter and the Cursed Child) might wind up contradicting some of what the fans come up with, but they will also create their own hitherto unnoticed nooks and crannies in which fans can create their own works.
Twitter is actually perfect for these kinds of author/fan interactions. A 140 character tweet is just long enough to convey one juicy bit of gossip about Harry and his fellow wizards but not so long that they wring all the mystery out of each reveal. They read like status updates from absent friends. They make us curious about what else our favorite characters have been up to in the years since the release of the final book.
These tweets exist in a weird place between canon and fan fiction, a strange border country that new media scholars and fan studies folks have lived in for a while. Welcome! Have fun exploring!