So, the article has some bad misinformation. GMK and Signature Plastics are two different companies, thick keycaps doesn't necessarily mean that the keycaps will be good at all. Hate to break it but ePBT is EnjoyPBT, both the same exact brand. For those that care, Akko keycaps are known for being clones (yes, I know not everyone cares about that). ABS and PBT can have the same sound signature. For ABS vs PBT, take the same thickness keycaps (measure with caliper and you can see same thickness), put them on the same build one after another and it could easily sound the same. Also lots of the plastic keyboards we use today are polycarbonate, so they are not ABS inside the case. If all the boards out there used ABS for their cases, we would see so many shined cases alone. The GK61X, and other equivalents from Royal Kludge, Ducky, Anne and more, are all plastic that isn't ABS or polycarbonate. I am mentioning those as they are the most popular boards to find when someone is looking at a board to switch out from their "gamer" one. I own a set of DCS keycaps, made by Signature Plastics, same place that makes SA keycap profile, and they may be thin but they do feel great. They are a quality feeling keycap that I would actually recommend to people although they are thin. I see that you mentioned with keycap thickness that it depends on your preference of what you like, which I do agree on, but when you mention "Keycaps with thicker walls often feel more solid when bottoming out and have a deeper sound when typing. By comparison, thinner keycaps often feel less substantial and have a higher-pitched typing sound.", this also has to do with the materials of the case to the keyboard, the switches (whether they are lubed or not), and also the materials of the plate used.
Another thing you mention in the article is a whole bullet point on PBT being better than ABS in longevity. This is not true. If you are only going on keycap shine then that is true. If ABS really wasn't good for longevity then why do lots of the popular gaming brands use it as their stock keycaps.
You mentioned also Romer G and Topre as two more limited options for finding keycaps. The only options to find for Romer G would be replacement caps just for the gamer buttons. Otherwise, you are stuck using the stock keycaps on a Romer G board.