I was browsing SnitchSeeker.com due to a new J.K. Rowling project/game that J.K Rowling is holding right now. In the thread, this was mentioned by a member:
We've known that something had to be added for DH and Teebin mentioned "getting a confirm that something specific is going on regarding expansion", but this is the first time that I've heard about anything happening on the anniversary of the WWoHP's opening (June 18th, 3 days away). The Weasley twins were also in the park recording something that is still unknown. I realize this is an employee/ VIP tour guide's statement and they aren't always reliable but I thought it was worth mentioning.
UPDATE: It appears that the ten-letter clue in Rowling's game has been discovered. When moved around it appears that it states "More Potter or Potter More" (probably the first). Rowling also stated that even though this new announcement is not a new book, it is something equally exciting.
Here's the thread for those who are interested:
http://www.snitchseeker.com/harry-potter-news/updated-j-k-rowlings-secret-street-view-82202/