On Amazon right now there are listings for three new books under a banner called "Pottermore Presents". They look like three themed volumes of writings from J.K. Rowling about the world of Harry Potter collected from the site. Image: Pottermore
A search of Amazon brought up all three ebooks, each with a publication date of 6 September 2016. All three are about Hogwarts, but only two promise "short reads originally featured on Pottermore.com with some exclusive new additions." Hogwarts: An Incomplete and Unreliable Guide is only "short reads originally featured on Pottermore.com." It's literally about the castle the school is in and its "permanent residents".
There is also Short Stories from Hogwarts of Power, Politics and Pesky Poltergeists, which is apparently a "glimpse into the darker side of the wizarding world." Namechecked in the description are Professor Umbridge, Ministers for Magic, Azkaban (not sure how that has to do with Hogwarts, but OK), Horace Slughorn and Slughorn's relationship with Tom Marvolo Riddle. And finally, there's Short Stories from Hogwarts of Heroism, Hardship and Dangerous Hobbies, which lists Minerva McGonagall, Remus Lupin, Sybill Trelawney and Silvanus Kettleburn (whom Hagrid replaced as a Hogwarts professor) as being among the subjects covered.
Image: Covers of the books from Amazon.com
Pottermore has confirmed that these books are real, including descriptions of the ebooks that are roughly the same as the Amazon descriptions. Harry Potter and the Cursed Child, which did monster business, was also sold by Pottermore. These new books aren't an unprecedented move. Plus, there was word earlier this month that NBC-Universal and Warner Bros. had made a deal to work together on "digital initiatives with J.K. Rowling's Pottermore, which includes the author's original writing".
Pottermore certainly seems to be expanding into something which actually makes Rowling money, rather than simply a place for fans to learn more about the world.