No I don't think steem will over take FB unfortunately, if it continues it's current path. Steem encourages longer blog like posts where as FB mostly consist of quick snippets, usually many a day. I think this is where the average FB user would find that STEEM requires too much attention to detail and professionalism to be a real disrupter.

However in saying all that, I still think STEEM will be hugely successful. But it's kinda like comparing Bitcoin to Ethereum. They both have their place and attempt to resolve different problems and both can be successful.