Steemit would definitely take over Facebook one day but Facebook would not be crushed to land.
Facebook has its own advantages, the interface is awesome and the people who want to chat in terms of friendship would never leave it.
Steemit on the other hand is booming like hell, once steem price crosses 10$ everyone put their eye in it. Steemit makes us to learn from people all around the world, it teaches the way one should build his profile and a lot!
But I guess Zuckerberg is wise and he would soon dive into crypto just as the way he took over Insta and WhatsApp.