I don't think Facebook can be replaced by a blockchain alternative the entire premise of Facebook is built on the centralisation of data, its essentially a directory with a massive data warehousing program to support it.

It is built on creating feedback loops and creating pockets on the internet for echo chambers and content bias curation, that's how they are able to keep their users on and engaged for that long and gathering as frequent as much data as possible on every single user.

Then uses that as monetization and sells it to the highest bidder.

A blockchain alternative would have to function in exactly the same way but offer financial incentives like offer users part of the ad cost back to the consumer as thanks for providing the data in order to disrupt facebooks business model

Which is not what I think Steemit will ever become, its more of a content marketing tool like a Medium or Tumblr