Never noticed it before but it seems that this portion of platinum's battle castle music:
https://youtu.be/DklZrXQtYK0?t=180
Was referenced in Unova's Route 3 theme:
https://youtu.be/MXqZsS5i044?t=15

I imagine it was in some way a reference to Caitlin becoming an elite 4 member in Unova, even if its not played when you meet her.

Also, a bit more on the nose is Wyndon's theme:
https://youtu.be/9K_KkmWK3K0?t=47
Calling back to Wedgehurst's:
https://youtu.be/mTS4Nf8Id4Q?t=44

Anyone else noticed any other musical callbacks in the series?