If something like this were to be adopted in the US, I think I could live with it. But I think it needs two additional strictures:

(1) no overly invasive (genital) contact for the opt-outs/manual search
(2) some mechanism (I don't know exactly what) to ensure that opt-outs are not punished by being made to wait an unreasonable period of time for the manual search, thereby being forced to decide between acquiescing to the scanner or missing their flight.

At least it's encouraging that, if adopted, the opt-out would not be removed as an option--ever.