Okay, so I decided to do some math and decide how the SSBP (Paradise) rumor correlates with new playable characters.
Brawl had four (Five if you count Zero Suit Samus) new playable characters revealed at E3 2006 trailer. There were fifteen (Sixteen) new characters overall. While this won't end up indicating the entire roster overall, if only one new character is revealed at E3 2011, we should expect three to four new characters for the game. And if Mega Man Volnutt is confirmed, we will have at least two or three more new characters left. Which one do you think it'll be?
I'm absolutely certain that if only three to four new characters are going to be in the next game, there will be only three third-party characters max, possibly losing one of {Snake, Sonic}.
Which leaves us with only Nintendo characters. Any one of {Ridley, Little Mac, Ray MK III, Issac/Matthew, Saki/Isa Jo , Bowser Jr., King K. Rool} could be in as I suspect that the new characters will be either villains and/or characters from new series. I think we'll get one new villain and three new protagonists. The latter I pick Little Mac, Ray MK III and Issac/Matthew, thought less likely choices such as Starfy, 5th Gen Pokemon, Krystal, new Fire Emblem character and Samurai Gorah (Last one is slightly contradicting, since he's a rival of Captain Falcon, but he's not a true villain either, plus he's also a popular request, so he has a chance) are also possible. As for villains, I think it's going to be Ridley since he's the most requested villain IIRC, but if he doesn't work, King K. Rool or Bowser Jr. are also strong candidates for the one villain.
So overall, I predict {Ridley, Issac/Matthew, Ray MK III, Little Mac}.