Pretty much why I think Mewtwo and Jigglypuff are coming back. Zoroark, the other X & Y starters, Victini, Deoxys, Gardevoir, Darkrai; most of the other potential playable Pokémon we have been discussing are Pokéball characters. The only characters with any shot left are Blaziken and Genesect, but how likely are they really? With Squirtle and Ivysaur's spots open, I cannot see how you don't give it to the other two? Especially when Mewtwo spearheaded the entire Mega Evolution mechanic (and soon after Lucario and Charizard) and Jigglypuff is the quintessential Fairy-type. Setting aside the knee-jerk reactions there really wasn't anything today that hindered any two characters ability to be playable aside from Squirtle and Ivysaur. Period.