Good point but it's not well supported yet. There's no mobile clients I know of that support it (let alone with agent forwarding which I really need for jumpboxes).
And of course once you do fido, you're back to the same issues around SSH keys that certificates are a solution to (as the article demonstrates). So moving to Fido is not a whole lot better than using SSH keys which work very well everywhere.
Also, another important point: I also use GPG a lot to encrypt files. It's great to use the same key (sometimes, for sensitive stuff I use a different OpenPGP card) and toolchain (always) for this. So I need it anyway, might as well use it for SSH authentication as well.
And of course once you do fido, you're back to the same issues around SSH keys that certificates are a solution to (as the article demonstrates). So moving to Fido is not a whole lot better than using SSH keys which work very well everywhere.
Also, another important point: I also use GPG a lot to encrypt files. It's great to use the same key (sometimes, for sensitive stuff I use a different OpenPGP card) and toolchain (always) for this. So I need it anyway, might as well use it for SSH authentication as well.