Steemit can't destroy facebook for a simple reason. Its not the same thing at all.
Facebook is a augmentation of your real life. You can add friend, fin them, know what they are doing. Invite them easily to make event in the real world. What make facebook so strong in the long-term is the "page" system plus "friend" system, both together on the same account. Reddit and steemit for example are just like the "page" system of facebook, there is no "friend" thing here.
I believe Steemit is more a twitter/reddit like.
And the fact you have to give your phone number to make an account on Steemit, WOW ! Where is the privacy in it ? If the state ask steemit about the phone number of a user what will happen ?
I really believe in steemit as reddit/twitter killer. And twitter must die, their "censor policy" against "free speech" is insane. On facebook if you are not a leftist you cant speak at all. You have to agree with the new "politic agenda" or you are a fascist.
Now i hope a new blockchain social network facebook-like will kill facebook, by literally make it seem "old".