1. Mewtwo is based on genetics. X and Y are chromosomes.
2. There is a new Pokemon movie coming out and it is going to feature Mewtwo. Pretty random seeing how Mewtwo hasn't been relevant anime wise since Gen 2.
3. It was posted on serebii, which is a very accurate site.
2. Actually, it'll feature Genesect. Mewtwo was most likely included to serve as a foil/counterpart for it, given that (at least anime-wise) they were both artificially created by evil organizations (one through genetics, and the other through cybernetics).
3. Serebii itself said it was UNCONFIRMED (as of yet), so we'll just have to wait and see...
2. Remember that Rayquaza movie?
Oh... you don't?
You know, the one called Destiny Deoxys?
Really, they announce a new movie starring some new pokemon, then reveal that there's some other pokemon in it that will "Co-Star" in the movie (Read: Steal the Show).
If this is true, then the movie WILL feature and star this new form.
http://www.youtube.com/watch?v=yItm3iAonVo Message board arguments in a nutshell.