who know bitcoin will become in 2018 i think its not possible it become 50k USD 
I don't think bitcoins will be 50.000 USD/ BTC in 2018, that is too fast although there is chance for it but it is a little chance, bitcoins will be 50.000 USD/ BTC about couples decades later, bitcoin's price in 2018 i think it will be hit around $3000 up to $5000/BTC that is because the activation segwit on bitcoin's network but if the activation segwit is fail bitcoins will be down.