@conceptual:
I think the reason why they are not using NiTi is because they don't need such a high amount of flexibility. As mentioned in the post before a formula one car has a wheel travel of 1/4- 1/2 inch. Together with the length of the a-arm this gives a deflection of around 1 - 2 degrees.
Furthermore the extreme elasticity of NiTi is due to a change in the cristal matrix from austenite to martensite under stress. When you take away the stress the matrix changes again from martensite to austenite. thsi change happens in a hysteresis, so the material behavior differs from one way to another. this would make it different to set-up the suspension in the optimal way. Pure titan has constand material characteristics and through this is easier to implement.