Many Sondheim shows have been filmed (Into The Woods, Sunday In The Park, Company, Sweeney Tood), so it wouldn't be a total shock, though I'd think if it were going to happen, we would have heard by now. That said, I'm clinging to hope. Since the film that was made was so awful, I'd think Sondheim would want to have this production filmed.
"It does me no injury for my neighbour to say there are 20 gods or no god. It neither picks my pocket, nor breaks my leg."
-- Thomas Jefferson