I understand for other tangible assets, a WILL can be written to be revealed when the time is right. But for Bitcoin, I don't know how this can be done as it may require revealing the secrete codes of the wallets or storage device. Is there any other way this can be done?
This is what makes Bitcoin different: the private key and passphrase. Of course, no one can open it if we don't reveal the keys before your death. It's not a good idea to transfer only Bitcoin money if you die because the majority of them, they will sell all Bitcoins located in the wallet. So, if you think you are old, I believe now is the greatest moment to teach them about Bitcoin. They may not believe you at first, but as time passes and you continue to teach them, they will develop an interest in Bitcoin. If you find someone who is suitable for Bitcoin wealth, you can transfer it to him before your death and advise him on what to do with it.
Why would you leave bitcoins with people who you think won't trust you? When leaving bitcoins, choose someone who will honor your trust. You may have held Bitcoin for a long time but your next generation may not have held Bitcoin for as long as you have held Bitcoin for a long time. If money is needed and your next generation doesn't have money then of course they will sell bitcoins. It is not uncommon to do so in cases of necessity. If your family is in financial trouble or in danger, of course if you are alive you would have taken that responsibility because in your absence your family has been in financial trouble so if someone in your family can save themselves from that financial trouble by selling your bitcoins then it is never bad. And no matter how much wealth we earn, that wealth is wealth but we cannot take it with us after death, so there is no point in thinking about what will happen after death, what you have done before death is the main thing. You just need to make sure that your bitcoins reach your next generation after your death.