The body suit concerns me. But I can understand why they're going in that direction considering the actress' health. I hope they manage to maintain that lithe silhouette that they achieve with prosthetics on skin.
I don't have an issue with Jennifer's body. I think she looks beautiful and healthy, athletic even. I even think her cheekbones are similarly structured to Rebecca's.
My main concern is with the design of the character itself. One of the film series greatest accomplishments, in my opinion, is the concept and execution of the design of Mystique. She's looked deadly and alien and sexy all at once. But in X-Men: First Class, that execution seemed to falter. The biggest reason I can see is the fact that they painted the prosthetics the same tone as the skin below it. That caused the overall look to fall flat and we lost dynamics in the scales and across the body.
I hope they manage to bring the design back to the original concept and make it work with the body suit.