A dual caliper setup would serve no purpose other than increasing heat capacity through pad volume, although to keep weight down you would want to run the smallest parts possible. Theres plenty of torque output with a factory sliding 2 piston caliper so adding a 2nd caliper would only overbias the front of the car unless you ran very small piston sizes in them. In the end the system would be overly complicated and cost more to maintain since you have more components to worry about. The only time a dual caliper setup makes sense is in the rear when there is a separate parking brake caliper which has been used on Vipers for years and more recently on the Porsche Carerra GT.