First of all, this is a cool idea. I always love to see something private and encrypted. But I found some concerns and ideas about your project (and I think you may can fix these): 0. This has XSS vulnerability. If attacker writes down this memo: do_the_evil_things() and passes to people, they might be unknowingly attacked(get tracked by attacker their IP/Browser fingerprint, mine cryptocurrencies for attacker, etc..…
Appreciate the feedback!