I've been following the FIDO standard (a consumer-friendly public-key system similar to SSH key pairs) and it appears that it's close to being complete: both Google and PayPal have been testing it internally for some time, the just-announced Samsung S5 is compatible, and Yubikey has announced that the next version of their Neo product will be FIDO compliant.
I am looking to revamp my personal op-sec in the immediate future and I want to make sure the security token I buy will be backwards compatible with the FIDO standard. The xNT implant and the next version of the NFC ring will both be utilizing NXP's NTAG216 NFC chip, which has some secure storage capabilities. The xNT project lead stated over email that the xNT sticks to NFC standards so it should be compatible, however, Yubikey has stated that their current security tokens will not be forwards compatible with the standard.
Does anyone have any special insight as to what is required of the hardware to implement the FIDO U2F standard (why wouldn't the Yubikey's be backwards compatible, for example) and whether the xNT implant is future-proof? I don't understand why they couldn't encrypt the public/private keys for U2F and store the decryption key on the Yubikey.