I don't really understand what the term "protocol" means in this context or how a protocol can provide the foundations of a social network. Can you elaborate?
Protocol is the thing that makes sure you can get email from anyone, independent of what client they used to send it and what client you used to receive it.
There's technically nothing to prevent sending messages from facebook to twitter etc, those companies just didn't want it to happen so they didn't agree on a way to do it, that is a protocol.
While Facebook and Twitter may not have collaborated on a protocol for distributed social networking, other interested parties have, and they've come up with standards like this:
Whether Facebook and Twitter end up supporting such a standard may well depend on how expansively the European Court of Justice interprets the right to Data Portability that is being introduced by the GDPR:
Certainly when read in the light of existing competition law (not to mention the bad reputation Facebook in particular has right now, nor any cynical political protectionist goals that an EU court might have), it is possible that large near-monopolistic American social media companies may end up being forced to allow automated pushing of user's posts to friends on 3rd party competing websites.
The problem is that it assumes that people in general understand and want to use protocol based services because they are protocol based services. Look at instant messaging as an example of where consumers/users vote routinely to choose features over the foundation of the service. I would love to chat with people on XMPP but I don't know anyone who uses it.
Sure, it means that there would be a set of rules for social platforms to connect with each other, or people to connect to each other. The implementation is open for debate, but the general gist of it is to allow competition by not excluding users that are on different platforms. Blockchain technology for example, is protocol heavy, and different software (wallets etc.) can be created for it without excluding users.
