Maybe you could. Twitter and Tumblr seem to be about the same modulo the length. Isn't the advantage of Twitter its shortness? Maybe we'd discover what the advantage of Twitter is.
And perhaps Facebook is the same just with better networking features. Maybe we should try to write federated Facebook and Twitter clones to prove it can be done.
Whether or not such a requirement would be good for privacy is an important question.
The list doesn't help if your friends aren't on the other network. HN loves to come up with technical solutions to the problem of Facebook when it largely isn't a technical problem, it is a social one.
Imagine, which Google+ launched, how things might have gone if 5% of Facebook users could have moved their own social graphs to G+ with two clicks of a mouse. If everyone had 100 friends, and those friends were uniformly distributed (all stark simplifying assumptions), then a huge fraction of the global social graph could have been moved to the new network by a small fraction of the users.
Social media has no such incentive, so how could a regulated federated standard work? Even if it could, who would pay for / provide the development? The social media companies certainly wouldn't (https://xkcd.com/927/), and governments wouldn't for largely the same reason.
That gives Facebook engineers a year to design and implement a federated API that would work seamlessly. If reasonable and non-discriminatory licensing was required on the API standards, then possibly others could interoperate with it too. Hopefully the mini-Facebooks could start to differentiate themselves through features, price, privacy, etc...
Needless to say, I think even if congress ordered facebook to breakup, it would be cheaper and easier for Zuckerberg to just move everything off shore and thumb his nose at a relatively impotent body. Zuck could also just lobby his ass off and probably end up writing the laws for the congressman.. Unfortunately, business writing the law for itself is pretty common in the USA, I'm sure Zuck knows that.