Ridley wouldn't fit in at all, people. He's far too large, (like, three times the size of Bowser) would look clumsy and stupid on the ground and just wouldn't fit in with the other fighters. Let's just be happy, that he's included as an unplayable character.
Anyways...
Likely:
Little Mac.
Another character from Pokémon. (Preferably Gengar or Alakazam, but I doubt, that they'll add any more gen 1 Pokémon to the fray.)
King K. Rool
Might get added:
Another Sonic character. (Knuckles or Shadow would probably have the most interesting movesets.)
Yarn Kirby
Wolf Link (Could be kinda like ZS Samus or Sheik.)
Unlikely, but would be pretty cool:
Travis Touchdown
Mega Man
Simon Belmont
Characters, that I want removed from the game:
Jigglypuff
Ice Climbers
Most clone characters. Or at least give em' a moveset of their own. (Even though Ganondorf and Toon Link are my favorite characters.)
