[alanpost]

We use Yubikey for our production systems and yes: every operator has two keys that have been configured and registered in our access database.

We decided though not to make our backup keys hot. It's a manual operation to enable it. The risk that everyone could simultaneously lose their key was lower than the risk of a backup key being lost and then used--since a person isn't likely to routinely check on their backup keys the later problem may go undetected for some time, whereas you know the day you lose your primary key and must report that situation anyway.