I agree with you! I mean, it would have been great to see it in the books, but it was sort of implied and I'm really glad she chose to say it in such a huge forum.

We don't really know what she intended, or if this was part of the overall story from the moment she mentioned Dumbledore's battle with Grindewald. We'll never really know, so why insist one way or another? I think it's better late than never! Plus, these books are going to be around FOREVER, and every generation of kids is now going to read them with this in mind. I think that matters.

I wonder if this bit of info will make it into the HP encyclopedia? That will surely make it canon.