Assuming at least 50 updates to go, and roughly equally split between items, assist trophies, characters, character moves, final smashes, music, stages, single player information, Pokemon and game modes, there should be minimum five of each.
So, five characters. Ness, Captain Falcon, Luigi and Jigglypuff are almost for certain because of being in the original. That doesn't leave many "slots" left and we still haven't got Falco, Young Link, Mewtwo, Mr G&W, Ganondorf, Marth, Roy or Dr. Mario in there.
I'd say that was an indication very few truly new characters will be revealed between now and NA launch in December.
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