Interesting, I never knew there was a private key for bitcoins that can be passphrase encrypted. Well if this is the case then this might be a safe way to create something like this since the private key will not only be the one needed to open the wallet. Though I guess a lot of people will still be skeptical to give out the private key though, but I do think this could be an alternative to Cryptosteel which was also a kickstarter project.