(Re-created because #1997 developed into a different discussion.)

How much effort would be required to add such a support? The aim would be to not force the user to use OpenPGP-compatible smartcards/tokens. There is a gnupg-pkcs11-scd project, but I'm unsure how feasible it would be to incorporate it.

I hope this isn't too ignorant a question — unfortunately, I'm not very good with technicalities.

The main reason for this feature request is that smartcards, like Smartcard-HSM, support PIN pads, which makes them a bit more secure than typical USB tokens in my view. I know that Nitrokeys are used for HOTP verification, but as long as I'm not convinced that my concerns with HOTP (again, see #1997) are invalid, I see TOTP as superior for users.