“The performance date may be news, but the subject is well known. Written with the playwright David Ives (Venus in Fur), the piece is based on two films by Luis Buñuel, The Discreet Charm of the Bourgeoisie and The Exterminating Angel. The first, in Sondheim’s précis, is about a group of people trying to have dinner together, and the second is about people having dinner together who for some reason can’t leave.” (The hope is for the musical to run in New York at the same time as Thomas Adès’s new opera version of The Exterminating Angel.)