Correct me if I'm wrong, but the impression I get from Standard Oil and Bell is that each big company essentially just had to duplicate its administrative tier and give each one its own branding, and then things (mostly) continued on as normal at the subsequently carved-up logistical and physical levels.

It seems to me that if we were to change Facebook from its own platform to an XMPP- or email-style federated network, then such a network would have to be constructed in the first place.

Not saying it can't (or shouldn't) be done, but I do believe it is a more complex example than Standard Oil or Bell. We've also got international borders and regulations in the mix.