I have a new perspective towards what it means to keep things private. I am thinking that keeping things private does not always mean keeping things to yourself. Before you criticize, I know that to have someone as trusted as that is rare and almost impossible, but they still exist, and sometimes you can find that person in your spouse. If you can share important details like passwords of bank account or safe, or grant them access to important documents, should we not also be able to trust these people with access to our bitcoin wallet?
I can chime in here as this is a major part of what I do in my career. I also collect physical bitcoins and it's a topic that I created "if you died tomorrow, what would happen with your physical bitcoins, would your family know how to sell them, etc".
So it's the same concept. There's a number of things you can do here. Trusts can be established, they can referred to as "control from the grave" where information is stored securely somewhere and is not release until one passes and it's not passed on to anyone but whom is listed in the trust. I think marriage is a raw deal and a horrible contract and never will get married. Why not just be partners ?
Trust is very hard to come by in it's truest form. In collectibles we've had so many "close friends", people we meet in person, talk to on the phone often who fuck us over. So be careful.
But no, thee is very littler difference between what you mentioned and your private key. Hell do it yourself, weld it in to a metal plate, put in a storage container that can be buried etc. I think smart contract will be able to help with stuff like this one day actually.