It seems to me as if something like this might be a reasonable idea, at least for some gear configurations. Basically, the concept is simply to tighten the shoulders by taking the slack through the waist belt.
Of primary importance to such a rig system is considering what becomes of the rig in the event of a buckle release. It appears that the system as posted (in both the special plate and the roller add-on cases) loses all shoulder strap integrity in the event of a buckle release. That could easily be addressed by adding a "stopper" to prevent more than a given length of webbing from escaping through the slide (or roller) should the buckle release. Having a stopper would prevent complete strap failure in the event of a buckle release -- although the shoulder straps will be extremely loose, they will still be closed loops, and the situation can be managed. For a simple failure, you'd merely refasten the buckle. For a total failure, it might not be the most comfortable dive ever, but you won't find yourself attached to your rig by only your mouthpiece.
Obviously, you'll still need to adjust the D-rings (hip and shoulder) to take into account the different fit between, say, a skin and a drysuit with fleece. You'd have to do those adjustments regardless of whether you used a traditional rig or a "sliding shoulders" rig, but given the ease of the webbing adjustment (i.e. practically nothing at all), you should make special note not to ignore the D-rings, lest they become useless at times.
(When the webbing adjustments are so trivial as to be virtually unnoticed, it's easy to get lazy with the D-rings. That's no more a problem with the system than having extra contingency gas in a pony is a problem with your back gas.)
I'd be interested in seeing something like this with no rollers, perhaps using a []-ring (i.e. like a D-ring, but rectangular -- 2 inches wide any maybe half an inch open). That would be narrow enough that a D-ring (or just a single-bar slide or "keeper") could perform the function of "stopper".
Of primary importance to such a rig system is considering what becomes of the rig in the event of a buckle release. It appears that the system as posted (in both the special plate and the roller add-on cases) loses all shoulder strap integrity in the event of a buckle release. That could easily be addressed by adding a "stopper" to prevent more than a given length of webbing from escaping through the slide (or roller) should the buckle release. Having a stopper would prevent complete strap failure in the event of a buckle release -- although the shoulder straps will be extremely loose, they will still be closed loops, and the situation can be managed. For a simple failure, you'd merely refasten the buckle. For a total failure, it might not be the most comfortable dive ever, but you won't find yourself attached to your rig by only your mouthpiece.
Obviously, you'll still need to adjust the D-rings (hip and shoulder) to take into account the different fit between, say, a skin and a drysuit with fleece. You'd have to do those adjustments regardless of whether you used a traditional rig or a "sliding shoulders" rig, but given the ease of the webbing adjustment (i.e. practically nothing at all), you should make special note not to ignore the D-rings, lest they become useless at times.
(When the webbing adjustments are so trivial as to be virtually unnoticed, it's easy to get lazy with the D-rings. That's no more a problem with the system than having extra contingency gas in a pony is a problem with your back gas.)
I'd be interested in seeing something like this with no rollers, perhaps using a []-ring (i.e. like a D-ring, but rectangular -- 2 inches wide any maybe half an inch open). That would be narrow enough that a D-ring (or just a single-bar slide or "keeper") could perform the function of "stopper".