That's interesting. They originally said that Mewtwo was genderless. But now they have a differently designed Mewtwo in this anime, and voiced by a female. Does that mean that there are two mewtwos? The original one being Male, and this new one with the transformation being female.
I think that's the only logical sense. Although it's still hard to tell if Mewtwo getting a gender is canon yet. Sure the anime is not based off the games. Tough in theory, if Mewtwo does have a new form, he would need to be included in the new X/Y games. If it turns out that this one gets a female gender in the game, than it will pretty much be canon, and that he finally gets a gender in this generation. Not that it would be necessary. Though I always imagined the original #150 Mewtwo being male. Not because of their VA's, but because the design of the character as well.