I have a OP/TECH USA Super Classic connected to the collar loops and usually carry the lens/body combo cross torso with the lens pointing down when I walk. It's pretty comfortable. I do occasionally use the foot as a handle if I haven't put the strap on yet, but this isn't very frequent.

My printer is enclosed, so ASA and nylon aren't really a problem to print. Designing the part with something non-printed running through it as a safety is a great idea.

Molding sounds like more work than it's worth for a one-off. There might be an opportunity for someone with the motivation to set up a really specialized shop making/selling these replacement collars, but I don't have the time to sink into anything I would want to charge $$ for.