The traditional objection to this sort of thing is that it creates perverse incentives: the government, or whichever body is managing our bystander/trolley tracks interface, benefits in the short term (smoother operations, can claim more people saved) if it interprets its numbers to maximize the number of warm bodies it has to work with, and the people in the parts pool benefit from the opposite. At minimum we'd expect that to introduce a certain amount of friction. In the worst case we could imagine it leading to a self-reinforcing establishment that firmly believes it's being duly careful even when independent data says otherwise: consider how the American War on Drugs has played out.