I just got off the phone with Ryan at Apple Support. He said he would get back to me later after looking into the situation, but I didn't get the impression from him that much will be done, if anything. He spoke about how relatively few people seem to be suffering from this problem, and that Apple would certainly be responding if the problem was much more common (but of course, that isn't the case, so....). I suggested that Apple should try 3-D printing some mockups of PBPs made from a few different but suitable materials and try them out on folks like us to see if they can find one that doesn't irritate our skin, but Ryan didn't think that was going to happen. I also suggested that Apple find out just how many people have had this problem (they must keep stats about such things). Obviously Apple wouldn't share such info with us, but surely they must have the numbers or how else would they determine if they have a real problem on their hands or not?
One other idea I have is to buy a pair of PowerBeats 4 https://www.beatsbydre.com/ca/earphones/powerbeats, the latest version of BeatsbyDre's connected-together wireless earphones, and give them a try in the hope that they're made from a different, non-irritating material. If they have the same effect on my skin as the PBPs, I'll be able to return them for a refund within two weeks of buying them. If they don't irritate my skin, they should do fine as they have a virtually identical design to the PBPs (the ear hooks!) except the two ear pieces are connected together by a single wire that goes behind the neck. I think I can live with that! :)