I dont think R.A.B. will be anyone we all know, but I guess its possible since theres only one book left
The hardest part is that the last book more than likely wont come out for a few years, at the very soonest next summer/fall

The only part that bothered me, is that Harry didnt try to use spells silently like Snape was saying, they never said whether he had mastered it or not since learning it came quite early in the book somewhat

Also Dumbledore is gone, but why dont they just question the new painting in the headmaster office instead of trying to interrogate Harry? Why doesnt Harry talk to the painting in fact?