It's been all over the children's lit websites. The publishing-industry media. The Muggle newspapers, and probably the Daily Prophet. J.K. Rowling regrets the Ron-Hermione pairing and thinks Hermione would've been better off with Harry.
(This post assumes that spoiler warnings for the Harry Potter series are, at this point, irrelevant.)
At first, the ship heard 'round the world sounded like another "Dumbledore is gay," but I realized quickly that this is something different, something even less powerful. The earlier revelation claimed that it had always been part of the HP universe's truth, just not overtly mentioned. It invited lots of "you don't get to say that now" objections, quite a few of them followed closely with "but why didn't you say it earlier?" And it would've been an amazing case of what I'm now seeing referred to as casual diversity if the series had contained an offhand mention of Dumbledore's orientation (more amazing for its not-that-long-ago time than it would be today). More focus on it than that would've been fascinating. Would Slytherins have been homophobic? Would the Ministry of Magic? Come on, J.K. of ten years ago, you were getting banned anyway. The after-the-fact announcement was something, but inclusion in the canon would've been something much stronger.
And this Hermione Steals Ginny's Man thing? I get why people are upset. If anything, I feel badly on poor underdog Ron's behalf. Harry gets everything; why shouldn't Ron get the brightest witch of her age? (I disagree with claims that Ginny lacks personality - the girl conjures a mean bat bogey hex, and she knows when to use it - but she's not exactly in the running for Ron.) What I think JK may not understand is that Hermione's choice of spouse isn't the major reason so many people were disappointed in the epilogue to Deathly Hallows. The romantic relationships in the series were sweet (and sometimes unintentionally awkward; who here didn't cringe at the monster in Harry's chest?), but they weren't the most important part of the story. So much of the anticipation for Book 7 was about finally finding things out, and the epilogue contained virtually no surprises. (Albus Severus. Cute concept. Poor kid.) Once we knew who lived, who died, who was good, who was evil, and who was Snape, we (okay, at least I) wanted to know what contributions these characters would make to the wizarding world as adults. Was Harry an Auror? Was Ron? What was a lone Weasley twin like? JKR answered some questions about the characters' career choices in interviews that got less attention than Dumbledore's sexuality, but I'd've loved to see the interesting stuff play out on the page, where it belonged. As others have said, who Hermione married can't have been the most interesting thing about her life after Hogwarts.
One thing that disappointed many in the world of fandom about the epilogue was that it paired off so many of the characters in traditional couples. In fandom's imagination, many of the characters were gayer than a Grindelwald (was Grindelwald gay?). To have the author come out of the woodwork to say that after seven years, what bothers her about the series is that Hermione married one guy rather than another guy feels heteronormative.
It sounds like JKR has personal reasons for her change of heart, and that's the great thing about fan fiction. Anyone can write an alternate universe fic and make the story work for him or her; JKR basically just did that in interview format. But if she does that, or Cath Avery does that, or anyone else does that, all it does is allow for interesting speculation. It doesn't change what "really" happened.