I wonder how many people would even buy a coin, that can become worthless at any moment (it's value would exist solely because of integration with Steemit).

As you can see, that could've easily been said about Steem for the past 2 years before platforms like DTube, DLive, Busy and Utopian developed. Not to mention that if steemit died the coin would drop it's price like crazy, possibly below 1 USD. You're delusional if you don't see the similarities of a potential Facebook Coin and Steem.