The messages would still need to be stored somewhere, right? Is SMTP a decentralized protocol in this sense? You can send a message from any client... however m

The messages would still need to be stored somewhere, right? Is SMTP a decentralized protocol in this sense? You can send a message from any client... however most people still use centralized solutions, not their own mail servers. In your example HN would still need to retrieve and store billions of messages, handle user authentication, discovery, aggregation, additional data handling (e.g. you want to attach a video, or go live). They will need to monetize _something_. So we are back to square one, just with a much more inconvenient client setup process (like we do right now setting up pop3/smtp/imap).