We can even imagine an email-based microblogging hack. Edit your boop (that's the new tweet) in your favorite MUA: the subject is the short text, the body is the long text. You can even put images and attachements in there. Send yourself this message, with a well-known prefix: it ends up in a specific IMAP folder. Have your third-party server that pulls messages from this folder and displays them in a "nice" view, so that anyone can browse and subscribe. To reply to boops, just reply to it in your MUA along with a copy for yourself and it will be present in your "Timeline" and in theirs. To address someone, send them a copy.
In a perfect world you could anonymously authenticate to anyone's IMAP server and read that "boops" folder, and even subscribe to it if you want. But I don't think any existing provider will ever implement something like that.
Email and RSS have all the fundamental building blocks for so many usecases already, but we keep reinventing the wheel again and again. The abstractions work. Imagine every company had to reinvent the whole TCP/IP stack every single time.