I am a fan of 500 Denier Cordura. In my experience, it is more than durable enough for my needs and it saves weight. UW Gear has been considering adding a 500D option to their line up for a long time now and I am glad to see them finally giving everyone a peek behind the curtain.
If they have enough interest to add the 500D option, the new rigs that result from the addition should be considerably lighter in weight. In addition to the weight savings that come from the lighter material, UW Gear has slimmed the harness where it meets the body of the rig for additional lightening.
If you are would like to see UW Gear add 500 Denier Cordura Nylon to their line as an option, let them know!