HC, a lot of people operate under false assumptions. I've changed my politics, religion, lifestyle, and much else when things stop stacking up. I'm sure I'll find out I'm wrong about more stuff. Yes, even cables, if something actually turns up.
However, finding proof of cables would be a nightmare for manufacturers and audiophiles. Since there are so many contradictory design philosophies, a discovery would probably show the vast majority of the market to be a fraud, if not all, save for the one design demonstrated to work. Most of the people who believe in cables probably are hearing placebo/suggestion. We just don't know which ones. Not all cables can work because of the design variations and the certainty that a percentage of cables on the market are frauds. Some of them are just assembled in a garage, never tested or anything, and just put out there to fleece people. Some manufacturers might be sincere, but some of them are just selling smoke and hype.
So if some evidence does turn up, it will not only validate that particular design/materials, it is also going to disprove pretty much everything else. I suppose it would just put the believers and especially the sellers, back in the position of arguing against facts.
As for testing people, you need to go more at the psychological expectations. Put a string of paperclips inside a Cardas wrapper and have someone "review" the sound. Compare that to a test where they listen to a known string of paperclips and then compare the reviews.
This not some deep philosophical thing or involving complex physics. It's people hearing what they expect to hear. It can be nailed down with some simple psychological tests. Discount those as "biased" or "unfair" if you want, but the results will be plain. Same with test gear. Nothing new needs to be developed or a new branch of physics developed. There are only three electrical properties: inductance, resistance and capacitance. If something changes electrical properties, you'll see a change in one of them. This is high school electronics, not something deep and mysterious.
I still argue that there is a lot of money to be made proving that there is something to cables. It is not just the audio industry that would benefit. If particular materials/construction really make a difference, there will be all sorts of industrial applications. Maybe you could improve the efficiency of electric motors. Maybe it would improve solar cells. Who knows? Lots of inventions get applied to other things down the line.
Also, a discovery would overturn known physics. Imagine that. There would be prizes, awards and lots of lucrative opportunities.