We were so very nearly there with U2F... I did extensive testing and you can have a U2F (Fido2/webauthn) device deriving it's private keys, never leaving the device's HSM, from a BIP-44/BIP-39 seed. You write 12, 18 or 24 words down (out of a dictionary of 2048 words) and with these words, you can always reinitialize another Ledger Nano (a cryptocurrency hardware wallet but I didn't care: I was after the U2F "nano app").
It just worked. It was beautiful. My seed were written on paper sheets which I'd store in a safe at the bank / at my parents' home, etc.
As a bonus the hardware device would display, on its little screen, if you were enrolling or login (a useful info) and, for known provides, it'd display the name. For example "login to google?" / "enroll to dropbox?".
Pure beauty.
Then sadly this trainwreck that passkeys are happened, greatly lowering not only the security of 2FA (someone is in control of all your keys and they can be "backed up": what a concept!) but also making you lose the ability to backup your own keys/seed.
I do really hope at some point we see a future "passkeys nano app" for hardware devices on which the user is in control of the master seed used to derive the keys. It worked for FIDO2/webauthn. I hope it'll work again at some point in the future for passkeys.
