If there are 50 characters, we have 18 left to be show
Jigglypuff
Ness
Captain Falcon
Falco
Ganendorf
Meta Knight
Wario
Ice Climbers
Mr. Game N Watch
Are more then likely to return, and Lucas, Wolf, and R.O.B are somewhat likely. That's 6 other new characters. If the rumors are true, with Shulk, Chorm, The Rhyme thingies, and Pac-Man, that leaves 2 unknown ones.