After 1 year, the keyduino nano is available! :D
You can found the board at elecrow for 25$ (here)
It's still a ATMEGA32u4 but I redesign the NFC antenna and add few ameliorations.
Currenlty I try some project like communication with a credit card, HCE communication, etc. If you have any cool projet to suggest with or without the NFC ring, tell me !