I cannot wait for this book to come out! Contrary to popular feeling, I am happy Fire and Graceling ended the way they did; it leaves readers with the satisfaction that the romance wasn't for nothing and the character's feelings were real, and a sense of reality, of not know how each ended. Most of the reviews I've read that have been against Bitterblue being the main character, I have found that almost all of the readers feel this way because they want to know how Po and Katsa ended. Newsflash:
THAT WOULD RUIN THE BOOK'S PURPOSE!
Katsa's whole character was against getting married, because in the world Katsa lives in being married gives your husband all the power, which she definitely does not like. It was clearly stated in the book that Katsa knew Po would give her what she wanted and all the freedom she wanted, but she still knew it was given to her, not fully her own. PO ACCEPTED THIS AND SO SHOULD YOU.
If Cashore went on to write that Katsa got married and had babies I would be hugely disappointed and aggravated, for, like I said, that is not Katsa's character at all. Cashore did a superb job with developing all her characters, and I am glad that is so, even if the romantic in me would have loved Katsa to be more open and lovable, almost like Fire.

Again, I cannot stress enough that I love where the new book is heading. If it has Katsa and Po in it, even better. I trust Cashore to do a wonderful job with this book.

EDIT: Now that the cover has come out, I have to say, it is beautiful! I'm looking forward to it even more!