On previous comments:
Yes, I hope they play Mercy Street, it's one of my all time PG favourites along with San Jacinto and Family Snapshot.
Also, regarding his last tour, Peter himself said they started to rehearse Supper's Ready for that tour , but it was abandoned.
I wonder why?
If this is his final tour (due to his age), is it such a long shot to think they may try it again given how highly he holds this (23 minute) song?