So let's play a game.
Let's say that the roster for the next installment was going to be incredibly big, and you were put in charge of the character roster. You would have to give every single franchise 4 more characters, (if possible.) Who would you pick?
Mario: Bowser jr. , Paper Mario, Toad, King Boo
Donkey Kong: K. Rool, Dixie, Cranky, Funky
Yoshi: Kamek, Birdo, Boshi, Baby Mario
Wario: Ashley, Mona, Jimmy T, Syrup
Zelda: Tingle, Vaati, Ghirahim, Onox
Pokemon: Mewtwo, Gengar, Scizor, Aegislash
Metroid: Ridley, Kraid, Sylux, Anthony Higgs
Kid Icarus: Paletuna, Hades, Medusa, Magnus
Kirby: Waddle Dee, Prince Fluff, Gordo, Galacta Knight
Gyromite: The Doctor Guy
G&W: Octopus
Ice Climbers: Polar Bear, FIsh, Condor
Pikmin: Plasm Wraith, Bulborb, blowhog, Dweevil
Star Fox: Fox's Dad, Slippy, Peppy, Rob 64
Fire Emblem: Anna, Robin, Chrom, Lucina
Mother: Jeff, Masked Man, Porkey, Starman
Punch Out!!!: Mike Tyson, Hippo, Mr. Dream, Aran Ryan
Mega Man: Protoman, Wiley, Elecman, Zero
Metal Gear: Raiden, Colonel, Otacon, Psycho Mantis
Sonic: Bluckles, Blails, Shadow, Big
F-Zero: Black Shadow, Goroh, Red Falcon, Fox's Dad
Animal Crossing: Tom Nook, Kapp'n, KK, Isabell
Wii Fit: Wii Fit Balance Board
It was hard to think of four characters for each series, especially since most of these won't even be assist trophies.