i don't believe that bitcoin can get up to 1 million USD in 2018 because, the rate at which most people are leaving the one that they have for investment purpose, and most people are changing there's to Altcoin, which have made the circulation to remain constant... the transaction rate alone have discourage most people to forget about it. so the growth of it into 1 million $ is not going to work in this year 2018
Even though there are people who are leaving from their investment in bitcoin and also there are people who are changing their percentage into other coin then it doesn't mean that the market capitalization of bitcoin will not hit 1 trillion because just take a look at the gold which is below the average for an asset if you will compare it in bitcoin but still one of the biggest market in the whole world.