so, we have HASHED TIME LOCKED CONTRACTS (HTLC) in bitcoin that works with the concept of PROOF-of-Payment and even could provide *reversible* transactions to the payer or re-route it to 3rd address. this only needs to open payment channels.
more info:
https://en.bitcoin.it/wiki/Hashed_Timelock_Contracts** if there are no other technical considerations, now we have an ALICE1-ALICE2-CHARLIE relationship in a dead scenario. Alice owns two accounts, Alice1 and Alice 2. Alice will have her bitcoins accessible by submitting a random digital content with Alice1 which triggers a transaction to Alice2. if this digital content does not submit before a specified future time, then could automatically re-route to CHARLIE.
It is unnecessary to use hashed timelock contracts if you can use simple a simple timelock value in transactions.
You shouldn't make things more complicated then they need to be.
Using timelock you will be able to use any kind of transaction (segwit, legacy,multisig) it doesn't need no special conditions.
Also you will have better support with more wallets and miners supporting it.
There really shouldn't be any need to complicate things like this. This is a very simple and old problem.
Why not just encrypt your seed with PGP, put the encrypted text in your will, and store the
password in your bank safe deposit box. You could even give the recipient a BIP39 password now, without the seed
so that only they can access the btc if/when the seed is decoded, presumably after you are dead and
your safe deposit box has been opened.
This should also work in it's own way. It is simpler to setup then using timelocks, although it moves a bit of complexity to the party that receives the inheritance.
It is also slightly less secure since it depends on trust of seed words not being obtained prior to the persons death.
So it's not as insecure as putting a private key in a will, since anyone would be able to steal it.
However from the perspective of a user that holds the password, the security is the same as if that was the private key.
So in conclusion, not as elegant, but perhaps easier to setup for the person that is writing a will.