I'm not completely convinced a federated protocol in and of itself will solve the entirety of the problem. I think we need some blockchain and smart contracts, people need to actually control their own data on these services. For instance, if facebook created an open source wallet, your data could sit behind that on your own device.
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.
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...