I recently returned from 2-1/2 weeks in Indonesia with my DSS steel plate and Torus 26 wing. The steel plate is ideal for diving with a thin to no wetsuit and an aluminum 80, as I only needed around 2-3 pounds of lead (in trim pouches on the cambands). This is not my first such trip, either. Sure, the idea of replacing in my baggage 4 lbs. or so of steel with a few more shirts or another pair of shoes or some souvenirs is tempting. My bag is right at 50 lbs. But the steel plate works just too well. Heck, you can always buy a clean t-shirt from the dive shop if you run short. The kydex plate sounds cool, but I LIKE the weight of the steel plate, and I don't like the idea of a weight belt if I can get away without one.
As far as "bulk" is concerned, I don't see how any other BC, such as those marketed as "travel" BCs, could possibly be less bulky. I remove the wing and fold it in half, just as it came to me in the mail when I bought it from DSS, and place it in my dive bag on top of my wetsuit, which cushions it against direct contact with harder stuff like the plate, lights, regs, etc. I am not familiar with other DSS wings, but the Torus packs as flat as a pancake (well, okay, there's the inflator hose). As I usually remove the cambands for packing and replace them at my destination, the plate too packs pretty flat--the relatively shallow bend helps--and the rest of the harness doesn't seem to really get in the way. The plate plus wing surely must occupy just a few inches of depth in the bag. All said, the BP/W packs much more compactly than my old back-inflate BC. I don't see how anything could pack more compactly than a relatively flat plate and relatively flat wing.