With an open standard, I don't see why you can't host your own social network similar to how people host their own email servers or websites right now.
> People don't use social networks because of protocols.
I agree with this point: usability is often not affected by what happens in the back. However, with open standards, it would be possible that people create other social networks because of protocols.
You mention all these technical problems that have to be solved to create a social network. I can see someone building an open source framework for all of these. For example with personal websites, everything except social graphs and feeds already exist.