I’m a lawyer who writes wills etc.

On death possession does not confer rightful ownership. What I mean is that when you die your assets (whether on a blockchain or anywhere else) will be distributed either by your will or by law, not by who you give possession to. You need more than a transfer. you need an unequivocal statement that you intend the person have absolute ownership. (You also need the ability to transfer that thing, I mean free of tax liabilities, relationship claims and the like). If you want to start an argument after you die, set up transfers of assets without any testamentary statement that courts will recognise. There’s obviously many hundreds of years worth of examples of reasons why this is required.