I believe, that in nearest future all social media will move their databases to one blockchain. And all of them become independent nodes and their databases will be the same (at least users content).
Only difference will be on the front end, where companies will show information that is preferable to their model (e.g. YouTube will show videos, twitter - short messages, Quora - questions and answers) and format.
Such approach completely change e feeling of social media. We will not be divided into different platforms, afraid to change platform and lose friends and subscribers etc. If we do not agree with terms of use (e.g. personal data policy) of one platform, we can easily move to another one, without any damage.
Blockchain will give us a freedom and this moment becomes very soon.