"I think it is a foolish idea to interpolate Surabaya Johnny into Threepenny. The song was written for Happy End. Would you include a song from The King and I in The Sound of Music or a song from Company in Into The Woods?"
I think Weill is the easiest composer to interpolate songs from other songs, because there is an underlying thematic element that connects all his shows - "Company" and "Into the Woods" are diametrically opposed, although.....
Imagine the Witch singing "Sorry Grateful" to Rapunzel instead of "Stay With Me" or "Agony" replaced with "Have I Got a Girl For You". And definitely Maria could sing "Hello Young Lovers" to Liesl after "Sixteen Going on Seventeen". And Anna could definitely sing "I Have Confidence" before meeting the King of Siam.
"The theatre is so endlessly fascinating because it's so accidental. It's so much like life." - Arthur Miller