J.K. Rowling is a silly goose. Why, after the release of the final book in her epic Harry Potter series, would she decide that it's relevant to add new information to the story? If anything, she's being self serving in an attempt to make herself look like she cares about gay rights. If she really cared, book 6 would have ended with an autopsy report revealing that Dumbledore had a rainbow cod piece on at the time of death. Book 7 would then have gone into some more spicy revelations regarding Voldemort's secret intentions for Harry.

I should really write fan fiction.

J.K. Rowling telling the world that her headmaster character is gay is about as irrelevant as her holding a press conference to tell the horde's of Potter Fans that Crookshanks falls victim to an unfortunate stage coach accident in Diagon Alley 5 years after Book 7. Nobody cares.