I don't think FIDO saying importing/exporting keys is important and them having to standardize it is the same thing.
The first and most straightforward reason is that we have no standard for importing/exporting passwords in or out of password managers, yet we manage to export them just fine. Each vault has its own proprietary format that's simple enough for others to implement as well.
But more importantly, WebAuthn makes assumptions about the characteristics of an authenticator at registration time. (And establishes continuity of those signals with DPK). Exporting it would be contrary to that.
Instead, with all these password manager vendors not wanting to be left out, and a good portion of the userbase either not being entirely in a single vendor's ecosystem, I can see cross-platform virtual authenticators like KeepassXC here becoming more common, and I don't think it's unlikely that the OSs will offer APIs to back these keys with TPMs/Secure Enclaves, and will allow you to replace the built-in passkey manager with a third-party, much like they do with password managers today.
I see it more in the purview of OS APIs than FIDO itself. The big, nontrivial risk here is that it involves establishing trust between devices across ecosystems so that they can share wrapped key material, and this introduces a vector for attacks. A user could more easily be tricked into trusting a malicious TPM that exfiltrates they passkeys, whereas single vendors like Apple can implement mitigations as long as all the devices are in their own ecosystem and they can use their own services for sync.
The first and most straightforward reason is that we have no standard for importing/exporting passwords in or out of password managers, yet we manage to export them just fine. Each vault has its own proprietary format that's simple enough for others to implement as well.
But more importantly, WebAuthn makes assumptions about the characteristics of an authenticator at registration time. (And establishes continuity of those signals with DPK). Exporting it would be contrary to that.
Instead, with all these password manager vendors not wanting to be left out, and a good portion of the userbase either not being entirely in a single vendor's ecosystem, I can see cross-platform virtual authenticators like KeepassXC here becoming more common, and I don't think it's unlikely that the OSs will offer APIs to back these keys with TPMs/Secure Enclaves, and will allow you to replace the built-in passkey manager with a third-party, much like they do with password managers today.
I see it more in the purview of OS APIs than FIDO itself. The big, nontrivial risk here is that it involves establishing trust between devices across ecosystems so that they can share wrapped key material, and this introduces a vector for attacks. A user could more easily be tricked into trusting a malicious TPM that exfiltrates they passkeys, whereas single vendors like Apple can implement mitigations as long as all the devices are in their own ecosystem and they can use their own services for sync.