Here is my prediction roster. I choose 55 characters because I thought the roster would be 50, but with Zero Suit and Sheik going solo, I changed it to 50.
I think the Gamtsi Leak will happen, but I believe that the Chorus Boys could be a mistranslation for Marshall.
I also have K Rool, Ridley, Mewtwo, Takamaru, Lip and Captain Rainbow as newcomers.
King K Rool seems to be hinted at by the Kremlings being in Smash run with other Nintendo All Star rivals. Plus the rumor of Chunky Kong being an Assist Trophy makes me think that there will be a DK newcomer.
Ridley seems to be hinted at, but if he was a boss, they would have probably then included Pyrosphere at the demo. Plus, I think it might be similar to ROB and Toon Link.
Mewtwo has been mentioned before by Sakurai, and is the second most popular Pokemon after Charizard. He uses his Y Mega as a Final Smash, because then both X and Y have a version exclusive Mega Evolution.
Takamaru seems to be getting a new game and had a minigame in NintendoLand.
Lip is the weakest character on my roster as now. Mostly she is for the Captain Rainbow trio.
Captain Rainbow is in because of the Not So Little Mac trophy. I don't think that they would include a trophy for that unless the main character was in the game.
If I had DLC spots, they would be Roy/Pichu/Dr. Mario/Young Link/Squirtle/Ivysaur and Isaac/Robin/Bandana Dee/Krystal/Black Shadow/Chibbi Robo.