I'm considering upgrading the microcontroller on U2F Zero to support more functionality. Some features that would be nice:

• More program memory.

  • Makes room for bootloader, configuration functions, and application to all fit in same firmware and simplifies the setup/flashing process. The current programming process could be greatly improved.
  • More room for other services. PGP, encrypted storage, bitcoin wallet, etc.
  • Crypto could be implemented in software and DPA countermeasures could be added. This is a double edged sword as it would become more vulnerable to software vulnerabilities.

• More interfaces

  • NFC and Bluetooth interfaces

A couple microcontrollers that I like:

• Silabs Pearl Gecko. It has a lot of program memory and has hardware encryption peripherals built in, including 256 bit ECC. I'm not aware of any other MCU with asymmetric crypto hardware that can be purchased without an NDA. No U2F interfaces though.
• Nordic Semiconductor nRF52840. Plenty of program memory and supports BLE and NFC. The NFC cannot be powered from a reader though and would need a battery. Bluetooth would need a battery anyways. There are no ECC peripherals so crypto operations would need to be done in software or offloaded to something else.

Thoughts/comments/questions?