I must admit, I really like the design of this new Mewtwo form, (if it is a new form). The long head, the purple fingers and toes, as well as the thin design looks really great, I think.
Personally, I don't think it is a Mewthree or something, but a new form of Mewtwo, since it looks very similar to Mewtwo with the colors and the tail, which has been moved to its head.
Mew and Mewtwo looked a lot more different I think, and why would the new movie has Mewtwo in its title, if the movie is more about a Mewthree?
This is a very positive announcement for me, and i'm looking forward to find out more about the new movie as well as X and Y details.