OK, so I'm sorry if this was brought up already or not, but I have a theory about the music theory.
The music theory is that series music indicates if a newcomer is in. If a franchise shows up with a music, we deconfirm any future characters. Music can tie into character reveals. I belive this theory is partially true.
Taking a look at the music tracks, there are 4 tracks that can be associated with a newcomer reveal.
Brinstar Depths -
Bomb Rush Blush-
Bloody Tears/ Monster Dance-
Gang-Plank Galleon-
Disregarding the fact that they are associated to newcomers, I believe that there is one more thing that unifies these tracks. The length of the preview. All of these preview tracks are around the 1:10 to 1:20 mark. Compare this to the other previews, that are normally around the 0:50 to 1:00 mark. There is however one anomaly in this group.
Main Theme (BOTW) is 1:17, but isn't associated with any newcomers so far. Maybe, Nintendo is hinting at a potential Zelda newcomer? (The main issue here is that the main focus in Zelda newcomers, is Skull Kid, and BOTW has almost nothing to do with Skull Kid. Then again, Solid Snake has to my knowledge nothing to do with Snake Eater, and Chrom isn't the direct focus of Fire Emblem Heroes, and Vega's Theme isn't associated with Ryu.)