Exporting passkeys is the single required feature for me to start using them more. The "anti phishing" push has really gotten a little too crazy. It seems mostly related to our legal inability to push security responsibility onto consumers.
Given that you don't strictly need to have one passkey per site, is this desire to move passkeys around a holdover from wanting to "export" your passwords? Because if you can export them, an exploit can too. I find passkeys rather more interesting when they cannot be exported from a HSM / key enclave / yubikey, but of course I need to be able to register multiple yubikeys per site, and a few of my accounts didn't allow for this so I ended up using my yubikey for TOTP since I can have the same seed on multiple devices.