Yeah, I remember those...
That could work, providing that there is contineous support of the spine along the back to prevent too much muscle action. One of the problems might be that this back support would need to be fairly rigid beween the chest piece and bucket, otherwise the area of the back opposite of where the hook is located would take a lot of loading. That rigidity that might make it more difficult to move around. Most windsurfers seem to have gone to lower placed hooks with the change in technique and technology.