I didn't think that a somewhat off-handed and light hearted comment would be taken so seriously, but I read your post yesterday and did some thinking over the past day. Most larger packs have pretty much standardized on 2" webing for the hipbelts. Sheaths can attach to the outside of the webbing (unless the webbing is integral with the particular hipbelt pads) or can sandwich between the webbing and the hip pad.
Shoulder strap carry is a bit more difficult. Again, many have standardized on 1" webbing, but there is a myriad of methods that attaches the shoulder pads. Some have the pads "floating" on the webbing, held in place by fastex rings. Sometimes the webbing is built into the base of the pad, and there is a section of webbing attached to the face of the pad for the sternum strap. It would have to be adjustable for the various attachment methods or location. I don't think there would be any way to work up a truly universal type of sheath system, as it would become more complicated and expensive than having something made up for a different pack or hydration system. The best to hope for might be categorizing something like, "Model C-1 will fit Camelback Rogues, MULEs, HAWGs, and standards made after 1998". (Camelback went to a wide-section shoulder pad in 1998.) Another example would be, "Model D-1 will fit Dana Designs Killer B, Arc Light, and Arc Flex models."
Hydration systems, since they're in between sizes, seem to have an even more bewildering array of webbing sizes and configurations. As such, each would have to be worked on in a custom, individualized manner, but since you do that for a living, Scott, you'd know more about the process than I would. If it's okay, I'll try to decide which of my several packs I use the most, and contact you privately (e-mail or phone) about commisioning such a project. This might be a fun and informative project for everyone here.