Ethically, it is not an acceptable trade off. Your question is set in the future, after the action has been shown to be a success. A choice made today cannot be made ethical retroactively because it turned out to be the right decision. And it is unlikely we can prove the action caused the success in any case, or that not performing the action might have been better (maybe a success tomorrow sets back a better approach by 50 years, causing many more deaths). The better question to ask is 'if beta testing might speed up the transition to FSD and it might reduce the number of road deaths, is it an acceptable trade off?'. At which point you are doing risk analysis and algebra. But given this is the mathematics of human life, you are still in a very dubious ethical area, and the usual answer is still no.