+Seperate Mii into three fighter slots
+(so two slots extra occupied)
+Meowth (long time coming, staple of TV Show, Mario has more slots but Pokemon sells far more units)
+Lucas (they wouldn't dare -_-)
-K. Rool (no longer relevant in the current series of games)
-Ridley (because he's scary to little kids, not because of size)
-Waddle Dee (unlikely, too small fry, Kirby didn't sell enough to warrant another slot)
-Takamaru (???)
-Random button (new way to random expected)
-Chorus Men (possible, but... how...?)
This would not work for the total slots I predict.
Theories:
Extra fox character for new Fox franchise
KOS-MOS for Xenosaga representation, as well as fanservice appeal (low chance, Shulk is a more logical character choice and they wouldn't traditionally add two newcomers from a series in one game)
Either Toon Link removed, or Windwaker HD sales celebrated by adding Tetra (or more laughably, Tingle)
Because ZSSamus has Other M features, potential for characters from franchise added (Most likely MB / Melissa Bergman)
If character slots are based on sales, Paper Mario and Monster Hunter have earned a spot
and... what about Dragon Warrior? Mobile sales of Dragon Warrior exceeded Kid Icarus: Uprising
Professor Layton would also deserve some recognition, as well as possibly a Brain Age item or stage