[pcthrowaway]

How would you send a message on ethereum that would be encrypted before hitting the chain, and could be decrypted after some amount of time, without being decryptable before that? Any straightforward approach seems like it'd just rely on an off-chain decryption key, which doesn't really make it any better than putting letters in envelopes with the dates at which they should be opened.

Sarcophagus looks like the closest thing available right now, but it's still unproven enough that I wouldn't really count on it working 20 years from now: https://sarcophagus.io/

Time-locked wallets solve the potential issue of transferring value at some point after death, but can't be used to transfer messages.. not ones which aren't readable at the time you send them anyway