Here's an interesting interview with JKR about the book. At first she seems a little amused at the idea of Regulus being RAB; however, at the end she really starts hinting that Regulus might come into the story some more. She doesn't really say much about Snape, other than she's not going to shut down the theory that he was working on DD's orders.

One the note for Regulus, it seems a lot of people are suggesting that he is still alive- that he is actually Stubby Boardman. We'll see I suppose . . .