My Roster for Smash 4 (49 Characters, being lenient here...):
(Imagine the select screen for Brawl. Now, imagine it being 10 down and 5 across, as opposed to 9 across and 4 down)
-Mario, Luigi, Peach, Yoshi, Bowser
-Wario, Donkey Kong, Diddy Kong, King K. Rool, Bowser Jr
-Link, Zelda, Ganondorf, Young Link (Toon Link as an alt. costume), Tingle (-_-)
-Samus, Ridley, Captain Falcon, Samurai Goroh, Captain Olimar
-Kirby, King Dedede, Meta-Knight, Isaac, Animal Crosser
-Fox, Falco, Wolf, Krystal, Ray 01
-Pikachu, Pokemon Trainer, Lucario, Jigglypuff, Mewtwo (revamped)
-Marth, Ike, Sigurd, Lucas, Ness
-Balloon Fighter, Pit, Ice Climbers, Mr. Game & Watch, R.O.B.
-Snake, Sonic, Megaman, Bomberman, Random Select
14 New Characters:
-King K. Rool
-Bowser Jr.
-Tingle...
-Ridley
-Samurai Goroh
-Isaac
-Animal Crosser
-Krystal
-Ray 01
-Sigurd
-Mewtwo (new moveset)
-Balloon Fighter
-Megaman
-Bomberman
-Ganondorf's moveset enhanced to include a sword.
-One of Lucas' specials changed (likely PSI Magnet), Final Smash becomes PK Love
I expect that the next Smash will be for the next system after the Wii. I expect Nintendo to use Blu-Ray discs, and leap way in front of the competition with their next system, which will return to serious graphical quality and mature gaming not really seen since the N64, so I would hope that they could fit 49 characters into a Blu-Ray disc...