[alphager]

> Another alternative is these messages are broadcast through a public and decentralized ledger.

There is no such thing as free computing and data storage. Involving the group of strangers that run public decentralized ledgers requires paying transaction fees. Decentralization in itself is a dubious benefit.

A centralized service would be way cheaper to run (so cheap that it could be free for the end-users) with perhaps a one-time fee for identity verification purposes. The technology exists since decades (X509), is proven in the field and usable today.