Ethereum may be able to reach above $20,000 for each coin but I think it will not happen by 2018 because many users still use Bitcoin(BTC) and some of the users of the Bitcoin just switched to its fork like Bitcoin Cash(BCC), Bitcoin Gold(BTG), Bitcoin Private(BTCP) and many others because they believed Bitcoin first and when they encountered some problems they chose to fork Bitcoin to address the problem instead of switching to another cryptocurrency like Ethereum, which is the second based on coinmarketcap but after some time I believe that Ethereum may be able to come near the price of Bitcoin or may be even surpass it.