Maybe, but the messages are centralized and can be censored or removed in your scenario. Zmsg, while just a proof of concept, uses encrypted memo field in Zcash

Maybe, but the messages are centralized and can be censored or removed in your scenario. Zmsg, while just a proof of concept, uses encrypted memo field in Zcash transactions. Once the transaction is confirmed, it is part of the blockchain. This can be useful, for example, for political protesters against subversive government.