The main question that remains unanswered is how portable passkeys will be among ecosystems: can I use iOS and Android and Windows and share a passkey generated on one among all three? Given that Apple has built an AirDrop-sharing method for passkeys, I hope FIDO’s broad compatibility includes sharing passkeys among operating systems, too.
If you're struggling to get your head around what like with passkeys will be like, Glenn Fleishman's breakdown is pretty great. As quoted above, he does bring up my biggest unanswered question, which is how locked in these passkeys are to your smartphone. For example, as it works in Apple's updates coming this fall, my passkeys sync over my iCloud account to my Apple devices, but there is zero way to get those keys to an Android phone if I want to switch. It's currently a major lock in feature that I'm sure will be ironed out one day, and hopefully someone like 1Password is able to help here if it's not something the platform owners build into their passkey solutions.