Not to mention that most of the power provided by modern PSUs come from the 12V rails. The 3.3 and 5V rails are almost vestigial at this point, no hardware actu

Not to mention that most of the power provided by modern PSUs come from the 12V rails. The 3.3 and 5V rails are almost vestigial at this point, no hardware actually runs directly at those voltages, so removing them would not have any negative effect.