I just don't get the point of an ultra-light backplate. So you save a few pounds on baggage weight and, if that few pounds was really the difference between having to pay a surcharge for extra weight or an extra bag, you have to pay a hundred dollars extra on that trip you already spent thousands on. And then at your destination you likely have to use a weight belt anyway. Also, if I recall correctly, my Fundies instructor pointed out the advantage of having at least some of the weight close to your back and center of buoyancy rather than hanging on a belt. When I travel for tropical diving, I take a steel plate and don't need any additional weight to achieve proper buoyancy with an Al 80 and thin wetsuit. We see questions posted frequently about using weighted STAs, how to bolt weights directly to a backplate, etc., yet I haven't seen nearly as many posts asking how to lighten a backplate. And if one wants a lighter backplate, say, for diving steel doubles at their destination (kind of rare) or pinching pennies on baggage, aluminum is a lot cheaper than carbon fiber and doesn't weigh THAT much more.
Really warm water where you don't wear exposure protection and a lack of bioprene. It isn't about saving weight during your travel. For a wimp like me, there are few places I wouldn't wear exposure protection.