I'm not convinced this is a good idea. Resident keys as the primary mechanism were already a big mistake, syncing keys between devices was questionable at best (the original concept, which hardware keys still have, is the key can never be extracted), and now you've got this. One of the great parts about security keys (the original ones!) is that you authenticate devices instead of having a single secret shared between every device. This just seems like going further away from that in trying to engineer themselves out of the corner they got themselves into with bullshit decisions.

Let me link this post again (written by the Kanidm developer). Passkeys: A Shattered Dream. I think it still holds up.