Another thing I learned to stop daydreaming about under the reign of birdsite: convergence.
Capitalism incentivizes services to compete and lock-in, which is why every corporate social site has their own crap version of e-mail and/or messaging.
Federated open source on the other hand gets more successful with collaboration.
What if Free microblogging platforms replaced "DMs" with e.g. XMPP? It's an unlikely engineering mountain to climb but it is at least plausible