FWIW, I use Fidesmo. Oversimplified, it allows you to copy your credit card's NFC chip into an accessory you wear. I use a ring but there are other options like bracelets or watch bands. No batteries, no devices, no wireless connectivity. It works anywhere an NFC card works, which here in Switzerland is more or less everywhere.
It requires that the card issuer support Fidesmo though. Many here do but I'm not sure what it's like elsewhere.
That's not how those NFC cards work. They are payment middlemen. They are full cards on their own and just pass on every charge to your other card. Just like Google Pay.
Sounds very likely. Perhaps if you are sufficiently big you could also get a small kickback from someone like VISA? Operational expenses must be fairly low.
The way I described it was oversimplified. Technically, it's more like your credit card issuer issues a new card with the same number and installs it on the chip in the accessory.
To be able to do it, you have to authenticate with your card issuer in a mobile app, similar to how you might when setting up Android Pay or Apple Pay. The mobile app then uses your phone as a bridge between the issuer and the NFC chip in the accessory so the relevant data can be written in a secure way.
NFC payments via Google Wallet running on my Pixel Watch 3 connected to a phone running GrapheneOS works just fine. I use this regularly. (It doesn't require Google Wallet to be installed on the phone.)
At least one of my cards required Google Play Services to have the location permission when initially adding the card though.
