Well I'm trying to see the roster in my head with no cuts besides Toon Link and Snake.
33+3(Villager, WFT, Mega Man)+1 DK rep+1 FE rep+1 Retro rep=39 (Mewtwo as a veteran secret character=40)
So with this (considering all transformation characters are merged into 1) We have 6 newcomers. Add another 6 newcomers and we get 45(not counting Mewtwo), the predicted roster size and we get the same amount of newcomers revealed during Brawl for the starting roster: 12 (counting Snake and Sonic as they were revealed before)The newcomer secret characters revealed after Brawl's release is 4: Wolf, Toon Link, R.O.B., and Lucario so 45+4 secret newcomers+Mewtwo=50
If we get 9 more newcomers then 50 is very likely. But will Sakurai add 9 more?
Here are expected candidates:
Dixie Kong or K. Rool(DK rep stated before)
Chrom(FE rep stated before)
Takamaru(retro rep stated before)
Not on expected list:
Little Mac (Popular Series)
Chibi-Robo(Miyamoto's Adopted IP FROM NAMCO BAMDAI but still 1st Party)
Shulk(New popular and "cherished by many" IP)
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Fill in those last 3 for yourselves