I have some knowledge about the next Super Smash Bros. game that I would like to share. An acquaintance of mine has some connections in Japan, and reluctantly divulged some information about the game. He also gave me some insight on the series's future.
- Some lower priority characters (Jigglypuff, Little Mac, Snake, and R.O.B.) haven't been worked on yet and are likely not to appear.
- Fire Emblem doesn't have any new representatives because Sakura didn't think Chrom or Lucina would work. Roy was almost brought back, but ended up being dropped.
- Ike will return. He was recently finished and was the last character Sakura finished before putting everyone else on hold (if there is time at the end of development before release work will begin on them). His design is closer to his Fire Emblem: Awakening design, and his sword is now a creamy white instead of the previous gold color.
- The remaining members of the original twelve will return. Ness is becoming less and less important to Sakura with each passing installment, but he wouldn't dare cut off half of Mother's representation.
- Pokemon Trainer returns for one reason alone: convenience. The team just imported Brawl's version of the characters and touched up the models. Generation six starters were considered to replace the original three, but it was easier just to keep the same characters.
- Mewtwo returns, as planned. They haven't really changed his attacks much, and is reportedly not buffed much since melee.
- Lucario was a high priority and is likely to continue in every game forward.
- Lucas, Wario, Diddy Kong, Faclo, Wolf, Ganondorf, The Climbers, Game & Watch, Meta Knight, Shiek (in moveset), and Zero Suit Samus (now easier to access in-game) are back.
- Several newcomers were proposed but ultimately cut: Hades, Toad (replaced by Rosalina and inserted back into Peach's moveset), Pac-Man, and Charizard by himself.
- Newcomers Ridley, Dixie Kong, Palutena, Shulk, Takamaru, and a secret character kept up high are the unnanounced newcomers.
- The Wii U gets a Mario Kart stage, a Kirby's Yarn stage, and an F-Zero stage, among others.
- The 3DS gets a Pokemon Staduim stage and a Star Fox 64 stage, among others.
- Scrapped characters Roy and Dr. Mario are now Assist trophies.
- The fifth game is already being worked on by Nintendo EAD, until Smash 4 finished development. They want it out for the next Nintendo console at launch.
- There will be a system bundle for the Wii U with SSB4 included.