With all the Mewtwo stuff, I find it really hard to believe that even after they include Jigglypuff (You know they will.) That they'll allow the Pokemon rep count to go over the Mario rep count, despite how popular Pokemon is they'd never put more of them in over their flagship series. Notice how they seem to tie in each game.
SSB 64 had Mario & Luigi, Pikachu & Jigglypuff.
Melee had Mario, Luigi, Peach, Bowser and Dr. Mario, With Pikachu, Jigglypuff, Pichu, and Mewtwo. Mario has more in this game but that's only because of the clone. Pokemon would only have three without Pichu.
Brawl cut Dr. Mario but otherwise had the same lineup for Mario characters, Pokemon dropped Mewtwo and Pichu for Lucario and PKMN Trainer, who if you really wanted to could be considered three seperate characters but because they share one slot I'd say they're one. Feel free to disagree, but in this game they're 4 to 4.
SSB4 adds Rosalina to the Mario mix adding it up to 5, so potentially we'll get one more Pokemon and that'll most likely be Jigglypuff because she's part of the original 12.
Yoshi and Wario don't count in the mix obviously because they're labelled as their own series.
Ridley, it could be Other M ridley, who from my knowledge didn't have a Meta variation. Nintendo seems to have a boner for trying to get people to accept Other M's designs and stuff since they're the most recent but who knows I could be totally wrong. I feel Samus is enough of a major character to hold a series representation up herself, ZSS becoming a seperate character technically makes two anyway, but it fits the whole "Lone Bounty Hunter" thing. Same with Captain Falcon in a sense.