The NFC Ring is fantastic in it's form factor, but the Yubikey Neo is superior in its functionality. I would love to have a Yubikey Neo in the form factor of the NFC Ring. Mostly, I want the U2F and PGP functionality. It would enable even more seamless PGP signing and decryption from my smartphone.
Personally, I care about this more than I care about contactless door locks or payments. I will probably buy a payment ring, too, when they are available. But U2F and PGP are functions that I already use on a regular basis and it would be great to make that more convenient.
Also, look at what Fidesmo is doing. It would be really nice to have a ring that could work in the ecosystem they're trying to build.