Among the subjects covered will be the method of creating a Horcrux,
the manner in which Peter Pettigrew gave Lord Voldemort a rudimentary body,
and the reasons for Florean Fortescue's murder in the sixth Harry Potter book.
On September 4th, 2009, fellow Harry Potter fansite The Leaky Cauldron
reported that J.K. Rowling, the author of all seven Harry Potter books,
was hard at work on the yet unnamed Harry Potter themed encyclopedia.
They reported: "(J.K. Rowling is) making family trees of all her characters"
for the encyclopedia
On September 13th, 2009, we heard from a lawyer of Christopher Little,
who handles the publication of all the Harry Potter books in the UK,
saying: "The encyclopedia simply remains something
Ms. Rowling would like to complete sometime in the future."
This is a vauge answer at best, and I think I speak for the Harry Potter fans
as a whole, when I say that a release date, even if it was set for 2015,
would be better then just keeping us in the dark about the whole thing.
But for now, unless new information is revealed,
we are to remain in the dark.