Yes sure, once the primary token is lost, the backup should be used to login into all of the services we used the primary one for. But it's not worse than if we

Yes sure, once the primary token is lost, the backup should be used to login into all of the services we used the primary one for. But it's not worse than if we had a regular U2F token as a backup: we'd have, again, to login to all services and revoke the primary token manually.