I think I have found a crypto currency that could work very well with the ring.
NXT is a new currency that does not use Bitcoins code and operates in a different way. Your wallet can be accessed anywhere from a browser or any NXT app. The wallet is unlocked with an alphanumeric security key.
The security key is chosen by the user when they first open the wallet and as this is the key to your coins it is recommended to choose a complicated key that cannot be guessed, in steps the NFC ring.
I have used NXT a bit and have had to keep my key in a plain text file on my phone as it's so long to memorise, I think many users are in the same boat. I'm going to start keeping the key on the private side of my ring and see how I get on. I'm sure with some integration the ring could work really well with this platform.
I would recommend that you store it also on something else (e.g. print it, store it on a memory stick) as the ring (like every other device) could be damaged and thus be unreadable.
I'll definitely check this out when I have a bit more time. It sounds very interesting although I'm not a huge fan of crypto currencys
I think using NFC ring for using Nxt is a perfect choice. Nxt devs will help you with any questions regarding integration. Right now, useful info about Nxt can be found here: https://wiki.nxtcrypto.org/wiki/Main_Page or whitepaper: https://docs.google.com/document/d/1BWVPUsyS6G4gIyPXNO_XFoszhzP6jJRGe8t--RtpMkY/edit