I've always wanted to ask this, but what types of additions would lead you to feel a series is complete in terms of representation? IMO:
DK: Character, Assist Trophy,
Wario: Wario Land content (**** it Sakurai)
Metroid: Metroid Prime content (Frigate Orpheon?)
Kirby: Modern content (**** it Sakurai)
Star Fox: Wolf
Fire Emblem: Stage, Assist Trophy,
Pokemon: Stage
Earthbound: Mother 3 content (New Pork City?)
F-Zero: Character, Stage,
ROB: Stage/Professor Hector trophy,
Punch Out: Assist Trophy,
Street Fighter: Assist Trophy, Guile's Theme
Let's see... if we're going all out and assume this is some kinda mystical Smash 4 upgrade for next gen
Main Mario Series: Waluigi, Daisy, Toad (captain, -ette or plain)
Dr Mario: Own Stage, Own symbol (da pill), Own victory theme
Yoshi: Poochie as some kinda helper
Wario: Retro Wario Land Stage, Overall Wario as a separate character
Donkey Kong: King K. Rool, Dixie, Assist trophy
Legend of Zelda: Toon Zelda/Tetra, Windwaker alt for Ganondorf, Pirate Ship stage
Metroid: Another character (Ridley, Stylux, Dark Samus I don't know), Tone down the heels
Kirby: Bandana Dee, Return to Dreamland stage
Star Fox: Wolf, Krystal, Stage based off of Zero, New Final Smash for Falco
Pokemon: Bring Back Pokemon Trainer with Ivysaur and Squirtle, ORAS Stage,
F-Zero: A new game.
Earthbound: Bring back New Pork City
Fire Emblem: Some Fates content, I dunno
ICE CLIMBER: DO I NEED TO SAY IT?
Kid Icarus: Luigify Dark Pit
Pikmin: Make Alpha his own character
R.O.B.: A STAGE DAMNIT!
Metal Gear: Bring it back. Buy it's smouldering ruins from Konami's death auction
Sonic: A stage based off City Escape, a second character (Want Tails but will accept Knuckles, Eggman, Shadow, Amy or Blaze)
Animal Crossing: More New Leaf Content
Punch Out: More music, Assist Trophy, Stage Boss maybe?
Mega Man: Mega Man X music and maybe stage
Pac-Man: Ms. Pac-Man as costume/clone
Street Fighter: Chun-Li, More Music