Nope. It’s never come up in an interview. She’s given a lot of clues about the next book, but what little she’s said about the prince himself is up above.
Given her love of twists and turns, it could anyone except Harry and Voldemort. She’s also said that Dudley Dursley is exactly as mundane as he appears to be, so that rules him out.
Other than that, it could be anyone. Draco could have a surprising family secret.
Or Tonks might really be a man 
Yeah, but it’s been a secret all these years. Even Hermione thought his size was just the result of an accident with an engorgement charm.
Still, he is a favourite, along with Slytherin, Gryffindor, and Lupin. And why not? Maybe Fridwulfa was some kind of giant royalty (although I think royalty among giants might just be the one who can bully all the others into submission).
All we know about Aberforth is that he runs the Hog’s Head Pub and that he has a thing for goats (!). Nothing in any of the books to refute your theory.
But our mystery man has only streaks of grey hair. Otherwise, it’s tawny. That colour combination is one I associate with Lupin. We’ve never heard what his eye colour is, but for some reason it’s often yellow in fan art (meant to look wolfish?). He’s never worn glasses, but he seems to be aging at an accelerated rate, thanks to his lycanthropy.
Also, certain words mentioned “loping” and “rangy” are often used to describe wolves.
I think it’s interesting we’ve never seen a monarchy in this world, because after arguing about the ministry of magic with some people on another board, I realized it looks just like British government if you assume that the Wizengamut is the House of Lords, and Fudge is both a peer and an elected official.
But we haven’t seen the king or queen yet, or even heard them mentioned. I wonder whose face is on all those galleons?
I think it would be interesting to read of the other Wizarding governments. There must be others because in Book 4 Krum says “your Ministry”, which implies that, at the very least, wizarding Bulgaria is controlled by a different government than wizarding Britain. Perhaps each national government is a wizarding counterpart to the Muggle government (perhaps there is a President of Magic in the United States).
I’ve read somewhere that Rowling might come out with an eighth book, an encyclopedia about the Harry Potter world. If so, it would be wonderful if she put in a ton of information about wizards and witches all over the world.
From what I understood (I read it on a website a year ago that was apparently verified by her but who knows) Draco only allies himself with Harry temporarily, I don’t think he’s ever really a good gjy. I didn’t fully read the OP before I posted though so I don’t think it’s at all possible for him to be the prince. It might be a relative of his though, who knows.
No, Fudge is the Minister of Magic, not the Prime Minister. His American counterpart would be the Secretary of Magic, or the Secretary of Magical Affairs, or somesuch.
But why would a book written from Harry’s POV include a detailed physical description of Remus? He already knows what Remus looks like. I think the person described has got to be somebody Harry has never met before.
He might, conceivably, be the New Werewolf, though – the one who was Arthur’s roommate in St. Mungo’s. (Hey, you can never have too many werewolves, especially intriguing male ones 
) But really, the description sounds more lion-like than wolfish to me, so I’m still pulling for Godric. (Too bad JKR has confirmed that Regulus Black is dead, otherwise he’d be my other top pick.)
We often get physical descriptions of the same characters in each book. I just came across one while rereading Goblet of Fire “One , with very bushy brown hair and rather large front teeth, was Hermione Granger.”
We’vwe had that information before. We don’t need it again. It’s for people who haven’t read the first books.
Well, he was in Gryffindor. What if he was not only the Half-Blood Prince, but decended from Gryffindor?
I have noticed that with the fifth book, Rowling has quit giving some bits of information that she kept going over in the second, third, and fourth books (Harry Potter learned he was a wizard when he turned eleven; his enemy was Lord Voldemort who tried to kill him that fateful night, etc). I think she figures if you’re on Book 5 or Book 6, you’ve read the other ones. And if you haven’t, well, you should.
I’ve been searching through my usual Harry Potter source, and due to site slowness, I’m not coming up with anything conclusive. I’ll try again later.
Rowling’s recent discussions about the nature of “halfblood” raised some interest for me in this regard. She made much of the fact that whether someone is a halfblood or a pureblod is really more a matter of bigotry than any hard and fast line. This makes me think that perhaps the HBP is someone who once fancied himself a pureblood, or was thought to be by others, but has, or will have, his understanding of his own identity muddied.
There’s only one character I can see that would work well with this storyline, one whom we are both fairly familiar with and yet whom we know very little in terms of his past or ancestry. Though, I can’t see him being called a prince.
Snape?
Not unless he’s had a makeover - tawny hair and bushy eyebrows…
Well, we don’t really know. The term may just be confusing, or Rowling may have changed premises after the first book, and was stuck with the name.
I’ve put way too much thought into this, and the more I considered it, the less plauisble it became that the Ministry for Magic was a branch of the muggle government. They run every aspect of wizarding life. They refer to John Major as “the muggle prime minister” – not, “our prime minister.” Plus, I really can’t see Major being able to pick a Minister for Magic.
Then there are the nightmare complications of taxation and voting. Either the muggles are paying for a branch of government they don’t see, or the money for both systems is being kept seperate. How could you apply property and income tax to a group most of the government doesn’t even know exists? And if wizards make up such a small percentage of the voting public, they couldn’t vote out the Minister. They’d be effectively under a ditatorship that ran every aspect of their lives, because they wouldn’t even have the option of trying to convince the rest of the public to vote Fudge out – they’re supposed to remain secret.
It makes perfect sense if it’s a parallel system, though.
It’s not 100% that the excerpt is the Half-Blood Prince, just heavily implied.
And of course, Rowling likes misdirection, so that’s always a possibility.
Maybe Hedwig is an animagus, and that’sd his human form.
Well, if Hedwig turns out to be a human in animagus form, then she would be female, probably very fair with either grey or pale white blonde hair. As the animagus form always looks very much like the actually person.
Personally, if Hedwig turns out to be anything more than just a really smart Snowy Owl, I will be really irritated. She could have helped Harry any number of times and didn’t.
It’s simple, the Half-Blood Prince is Remus Lupin. End of story.
Aslan!
He is not a Tame Lion.
I’ve always held a secret belief that Harry is descended from Godric Gryffindor. On my second reading of books 1-4, I caught the mention that Lily and James had lived in a place called Godric’s Hollow, and with the addition of Harry ending up with Gryffindor’s sword, the idea has pretty much been cemented in my head.
I know a lot of fans have jumped on the mention in OotP of Mark Evans, a Little Whinging kid that Dudley and his gang pounded on. I haven’t yet decided if I think the name’s just a coincidence. For all we know, Lily and Petunia had a brother that we don’t know about. Although, if the extended Evans family were in the area (and complete Muggles), there’s no reason I can think of that Petunia would be estranged. Of course, the Hypothetical Brother Evans could have married a witch or a squib, but then we’re forced to come to the conclusion that if there were another living Evans relative, especially one who was at least okay with the concept of magic, Harry wouldn’t have been left in Petunia and Vernon’s custody.
I think it’s most likely that the HBP will be a brandy-new character. A friend of mine suggested that possibly Krum is Bulgarian royalty, but I doubt Durmstrang is as halfblood-and-Muggle-friendly as Hogwarts.
If Aberforth is a prince, then logically so is Dumbledore. And I don’t think a halfblood would have been approved as Headmaster of Hogwarts.
(Just tossing out thoughts as they come to me now, please don’t look for anything coherent or cohesive from this point on. )
I really dig Fretful Porpentine’s idea about McGonagall being a widow, and the possibility of her having lost a daughter to the Order. (And I also dig her name, but never mind that now.) It also ties in nicely with Rowling’s comments about how the marital stati (statuses? statia?) of the teachers at Hogwarts is something that will be covered in the future. (I don’t recall the cite at the moment, but another recent HP thread had all the new Book 6 stuff in it.)
Regarding Grimmauld Place, I had it in my head somewhere that Sirius had likely left all his possessions and property to Harry. If I’m wrong, then it will probably go to the Malfoys, or possibly Tonks. I had a momentary thought that she would be disinherited because she’d been blasted off the family tree, but then again, so had Sirius.
And I agree that Dumbledore will likely go to the Great Quidditch Pitch in the Sky before the end of the series, quite possibly in a “straw that broke the Chosen One’s back” manner, giving Harry just the incentive needed to kill Voldemort or do something else daunting and dangerous.
I think I should stop now and do some work. :o