I may as well just throw this out there right now. Is Heaven and Hell too big to play this festival? They play NYC on March 30th, and do not have any further scheduled dates beyond that which I see. The last update indicated more dates would follow (including U.S. dates).
They, without question, would A) blow the roof off the festival, B) fit with the Saturday vibe, C) make everyone who didn't already make their travel plans "kick themselves for it", D) would be a band that I wouldn't blame Rob for not wanting to "jinx" the possible confirmation and E) are also a band that I could see it being difficult to nail down an answer from since all involved are probably incredibly busy right now.
They are the only band that makes perfect sense in terms of everything Rob has said so far. The only huge question is, are they too big to play the fest? I'd lean towards "yeah, probably", but you never know.
Jason