It's easy enough (not to belittle efforts that have done so) to store Passkeys in a password manager. The part that kills the flow and where it gets nefarious,

It's easy enough (not to belittle efforts that have done so) to store Passkeys in a password manager. The part that kills the flow and where it gets nefarious, though, is whether platform and browser players (Apple/Google/Microsoft/Mozilla) will allow 3rd party Passkey implementations to be selected/configured by the user as their preferred WebAuthN backend so that you can use your 3rd party implementation at login time when the website or app the user is using wants to begin a webauthn flow and lookup or create credentials. Google said they plan to play nice and support 3rd party implementations. When I asked Apple during their Slack Q&A event on Passkeys they said that have no plans to support 3rd party implementations at the moment. I don't know how Microsoft and Mozilla feel. I would be a lot more optimistic about the whole thing if platform players would come out and commit to allowing 3rd party Passkey managers. Otherwise you'll never be an option in the system "choose which credential to use" dialog when some website/app wants to actually do webauthn.