[cirrus3]

I really like the idea of that upcoming service. But, not exactly where you want to store a piece of information worth $2B. A good old fashioned safety deposit box in a Swiss bank or something and several layers of trustees would be more applicable in this case.

[zucker42]

I would use Shamir's Secret Sharing and split it up over multiple different physical and/or digital locations.

[paxys]

It isn't that much different from adding a beneficiary for your online brokerage account.