Basically the "ink" is "uniquely identifiable" because the way the ink is physically arranged creates a unique "signal" which could be considered an "ID". That's fine for cows and objects with no security or authentication requirements, but human applications require much more capability. The ink "ID" cannot be changed. It cannot do any processing. It cannot perform any security measures. Furthermore, if any part of it becomes deformed, damaged, or worn, the "ID" could also change.
Chips with storage and more capabilities like our xNT are already passé.. we're working on VivoKey, which is a security application processing platform - in short, it can run apps. You can install security, identity, payment, etc. software on VivoKey. It's orders of magnitude more secure and powerful than any "rfid ink" could ever be.