I know that in terms of security it is not good idea (as explained here: https://github.com/Yubico/libu2f-host/issues/45#issuecomment-337013420). But we can live with that.
Is there any extension of U2F or may be some version/manufacturer of security keys which allow to do that?
The feature our customer wants to have is simple. User have the same device for several accounts. The device gets stolen. User notifies administrator of the site about that and the admin needs to act on all the accounts where the stolen key was used. We need a feature on the key which would allow us to do that.
Currently we use Yubikey keys.