Symantec has released their recent discovery that the Stuxnet 315 code is manipulating an array of up to 186 drives. Congratulations, guys. We have reached exactly the same conclusion. (As proof that we reached it independently: The data that is written to the drives by DP_SEND is located in an array in DB 888).
This finding strongly points to a controller for a module in a gas centrifuge cascade. One reasonable goal for the attack could be to destroy the centrifuge rotor by vibration, which causes the centrifuge to explode. Vibration damping is a problem for these devices that is addressed by stabilization of the rotor. Assumed the stabilization is done by the 315, that’s your point of attack. Other possibilities would be to ruin the centrifuges by induced creep deformation, or to simply lower the quality of the product, i.e. denial of quality.