We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda suck...
Passkeys aren't a full replacement in my opinion, which is what DHH gets wrong. It's a secure, user-friendly alternative to password+MFA. If the device doesn't have a passkey set up you revert to password+MFA.
And the fewer times that people are entering their password or email/SMS-based 2FA codes because they're using passkeys, the less of an opportunity there is to be phished, even if the older authentication methods are still usable on the account.