So looking at the music theory, here are the remaining series without music and their likelyhood of getting a newcomer. Note: This is assuming it is true:
Star Fox - Unlikely
Pokemon- Likely
MOTHER- Possible
Kid Icarus- Possible
WarioWare- Unlikely
Animal Crossing - Isabelle this week I'd assume
Wii Fit - Unlikely
Punch-Out!! -Unlikely
Xenoblade Chronicles- Possible
Duck Hunt- Unlikely
Sonic- Possible
Pac-Man- Unlikely
Of those that are unlikely, my reasoning:
Star Fox- Krystal probably would have been the newcomer, but she is an AT
WarioWare- Ashley would have been the likely newcomer, but an AT
Wii-Fit, Punchout, Duck Hunt, Pac-man- No other notable characters in their franchises.
Of those Possible:
- Mother: Porky is a villain heavy, and could be a newcomer
- Kid Icarus: Hades is also a villain heavy, Medusa could be unique like Isabelle to Palutena (But would probably be an echo)
- Xenoblade: Elma is a fan requested character
- Sonic: Tales or Shadow could be considered new characters similar to Isabelle. Or perhaps Eggman is newcomer as a Villain heavy. Who knows.
Pokemon: Obvious with Incineroar.
So in reality it just leaves us with:
-Mother
-Kid Icarus
-Pokemon
-Xenoblade
-Sonic
As outlets for potential newcomers from existing franchises. It would be a shame however for popular characters like Bandana Dee, Magalor, or Skull Kid I guess (partially a reason why I hope it's not real, but it's been oddly working so far)
On top of this, the theory doesn't hold for new franchise newcomers, so characters like Geno, Isaac, Banjo, etc are technically safe from these updates.