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You will want to be sure that your assets outside of your POD accounts are sufficient to cover your debts and any tax liability, otherwise your creditors (or the tax collector) may come after those who received the POD accounts, which can be unpleasant.
Which brings up some other points which is in a lot of places your debts die with you. Except for debt that is covered by real property. i.e. the $5000 someone owes Chase MasterCard will die with them. The $50000 they owe on the mortgage will stay attached to the property. Taxes will vary. But, in some places you can't transfer the property till the debt is paid so the property stays in the estate till the mortgage is paid off. [Side note of real life I had to deal with this along with a friend for a place in Arizona. What a pain.] In other parts of the world other debt might follow the estate. In others it all goes away as you are required more or less to have insurance to cover property debt.
I think that is always going to be part of the problem too.
BTC is world wide, how do you create a setup that will work in all the jurisdictions around the world and keep up with them as they change. And so on. Along with contested wills, and other potential things.
Just because it can be done, does not mean it should be done. And then where do you draw the line?
But, this is drifting a bit OT, it's not about the ramifications of the
BTC transfer, but about the transfer itself.
I think it really depends on the specifics of the person's situation. It is probably best for someone with any meaningful amount of assets to employ an estate lawyer to draft a plan to have assets moved upon your death. An estate lawyer can advise you based on your specific circumstances how quickly and how much of your assets can be transferred. This is probably one reason why the OP's proposal would not work well, as what may work in some jurisdictions may not work in all.
In general, the location the person died determines the jurisdiction of any probate court, or any rules regarding limitations on the transfer of assets.