I guess I could buy a safe and do it the way you suggested, but it still does not solve the problem with forwarding the safe password / code to the beneficiary in the first place. Neither does it make the regular updating of all the accounts and passwords more convenient.

And there is even the problem, that at the current state of "wild-west-crypto" I can't let my wife know, that I am 'playing around' with our money in this 'big experiment'. If I get a safe, she would want to have access to it from the start and she would find out and worry unnecessarily all the time.

So the only way to really make this work effectively would be depositing this letter at an attorney, notary or a bank box. And that is neither free nor convenient. So I'd still prefer to have a smart contract with an effectively timed trigger to pass on this secret to my inheritors.

Or to put it other way - just because we can ride horses already it does not make the development of cars unnecessary ;)