MASS SPECULATION TIME
Ok, lets assume all but one newcomer has been revealed, and all of the returning champions have been revealed...and that those 24 character comprise our starting line-up. Lets also assume that completion of the game with a specific character unlocks one other character, for a total of 48 characters. Additionally, finishing the game with everyone (unlocked characters as well) will net you one more character...a total of 49. The 50th character comes from completeing adventure mode.
So, who all gets unlocked?
Mario - Olimar
Link - Wolf Link
Kirby - Ray
Pikachu - Jigglypuff
Fox - Krystal
Samus - Ridley
Zelda - Ganon
Bowser - The Knee
Donkey Kong - K. Rool
Yoshi - More Yoshis...lots more
Peach - Luigi
Ice Climbers - Ricky Winterborne
Pit - Simon Belmont
Wario - Ashley
Zero Suit Samus - Kyle Hyde
Ike - Marth
Pokemon Trainer - AC Townsfolk
Diddy Kong - Dixie Kong
Meta Knight - Viewtiful Joe
Snake - Sam Fisher (just to see them fight)
Lucas - Ness
Sonic - Nights
King Dedede - Bomberman
49 - Mr. Game and Watch
50 - Dr. Kawashima
OK, ok, so I was bored...but hey, I can dream of a 50 character roster...