I am not the most knowledgeable about the fine details of the Proton Pack despite being a fan of Ghostbusters for around ~35 years although I can look at reference photos. I also don't own a 3D printer.
I DO own a Haslab Proton Pack and I have made numerous 3D plastic and metal toy accessories and replacement parts through my Shapeways store, mostly for Transformers.
I'm also generally committed to only modding my Spengler pack in ways that are reversible. None of us are getting another so why make mods we might later be unhappy with?
I'd like to brainstorm with you what specific parts you'd like to see for mods.
Thoughts off the cuff:
Stainless steel faux Clippard elbows with a brass finish that can attach to real wires on one side and the pack on the other.
A custom set of fittings for the ribbon cable that retains pack functionality while allowing people to attach real or 1:1 scale replica ribbon cable.
A new front to the Ion Arm with faux screws on the front restored. Unscrew the old one and screw in the new front. Save the old screws and front for reattachment later if you want. Made in HP black nylon plastic which has a finish similar to the pack and generally has a lot of flexibility and good applicability in mechanical uses.
A full size V hook bracket that has screw placements to use with existing screw placements on the Haslab pack. Based on my guesses, real pack V hook brackets have different screw placements and the BOK bracket, which does have matching screwholes, is smaller than a screen used one. Available in a variety of steel finishes including black and stainless.
Custom brackets for mounting an LC2.
In general, I'm looking to avoid directly competing with GBFans and established prop makers. I'm not looking to replicate anything that can easily be had at a hardware store unless there's a lot of demand for wildly different specs like thinner, screen accurate washers.
Shapeways can be expensive. I'm not a professional, just a guy with a theater degree who did the bare minimum in a scene shop 10 years ago and a toy enthusiast. The advantage to made-to-order 3D printing through a third party is getting bespoke parts, especially in fancier materials like HP Nylon and steel without the need for finishing to remove things like print lines. Somebody with a 3D printer can do cheaper prints from home.
As a benchmark, I'm guessing a V-Hook bracket will be about $60-80 plus shipping. That's generally not cheaper than getting one machined but it won't ever go out of stock and should fit to the millimeter. Probably $15 each or so for the fake Clippard elbows.