It's an unnatural restriction. Email has no such restriction! In fact, email has gone on to break many of its restrictions, enabling attachments, inline image

It's an unnatural restriction. Email has no such restriction! In fact, email has gone on to break many of its restrictions, enabling attachments, inline images, HTML formatting, and more. But lets say that the 140 character limit is desirable... Have a protocol for statuses (short) and posts (long) and networks that can only handle the short ones get links to the long version. As for public/private... Anything posted as 'private' wouldn't end up on public-only networks. That's a limitation that network has chosen, and they'd have to live with it. Email has adapted to users' needs, instead of laying down rules and refusing to budge. If there were a social networking protocol that was widely adopted, anyone who didn't adopt it would slowly die out... Unless they found some way to differential themselves that other network couldn't copy. And really, what couldn't they?