I'd love to have a ring that incorporates Yubikey like NFC functionality, I was worried it could allow login when I didn't intend it, but the idea of a switch might work. Having a USD dongle for hardware that doesn't support NFC but can negotiate the handshake between my ring and the device could work.

I'd buy a ring with just authentication, if it was rechargeable and did a few other things (pulse, sleep monitoring, etc.) even better, but the bare bones would be amazing so I could have something I wear for my authentication.