I've always wanted the Shibutanis to skate to Yo-Yo Ma's "Sakura Sakura", a modern interpretation of a traditional Japanese folk song.
The dynamics in the piece can show off their range, the song is quite different from what they skated in the past three seasons, and the song is 4:22 long so it's easy to edit. Most of all, it's different from what every other team does or would do.
I think the Shibutanis should go down the route of spiritual elegance, with programs that show off non-romantic beauty, the pure bond between sister and brother. Pieces like Meditation from Thais, which S/Z famously skated to, Chopin's Nocturne Op. 9 No. 2, or Clair de Lune are along those lines.