(This comment was posted when the linked URL was https://www.apple.com/newsroom/2022/12/apple-advances-user-s..., which contains the physical security key announcement as well as the E2EE stuff. If there's a better URL for the security key announcement, we can factor this topic into its own thread, since it's a minority topic in this one and mostly getting overlooked.)
That's what I am most looking forward to. I hope they also allow you to disable the phone-based recovery scheme that is just a boulevard for SIM-swapping hackers to breach through.
Given they already support standard WebAuthn (passkey or other), I think it’s a pretty safe guess to say they’ll support Yubikeys. I can’t find any written confirmation yet though.
I don’t think this is directly related to the E2EE announcement, rather it is an option to replace the current MFA method of receiving codes on your Apple devices.
The section of the announcement is emphatically about 3rd party security keys support, so the worry about lack of support of YubiKey over some push for some imaginary Apple Dedicated Key didn't make much sense to me.
Also, security key (at least to me) implies a small, keychain sized device. I wouldn't think of calling my Mac Studio a security key. There is no device marketed as such, even though yes, the SEP can and has fulfilled these purposes.
I hope they will support existing Yubi-Keys etc and not force users to get the dedicated Apple hardware key.