steve, ideally the ban would stay in place forever. If this is successful then the WTS would need to overhaul how they conduct their ministry generally and i believe that there is a pressing need for this. Plus child abusers should be banned from the door to door work completely. They shouldn't be allowed to participate even if another witness accompanies them.
In theory there is ample opportunity even now for jw children to be abused on the ministry. For example close friendships with JW youngesters can be formed and consolidated on the ministry and this can lead to greater intimacy. But it would be much harder to ask the goverment to regulate within the congregation and amongst JWs themselves. But I think the public interface has a chance of success.