One thing I'd like to see in the new game is unique victory animations for certain teams of characters.
The animations don't have to be just for characters with canon relationships (i.e. Mario and Luigi, Link and Zelda). Characters with relationships established in the Subspace Emissary (like Pikachu/Samus [both forms], Link/Pit, Luigi/Ness) could also have team victory animations of their own, as can characters that have relationships established in a possible story mode in Smash Switch.
The animations don't have to be just for characters with canon relationships (i.e. Mario and Luigi, Link and Zelda). Characters with relationships established in the Subspace Emissary (like Pikachu/Samus [both forms], Link/Pit, Luigi/Ness) could also have team victory animations of their own, as can characters that have relationships established in a possible story mode in Smash Switch.