A lot of crypto newbs have been feeding the whales. 5k ETH by 2019 is my prediction assuming the US economy and stock market stays strong.
I think it'll take longer.
Within this year, Eth HODLers will be fortunate if it gets back to $1400 it was just 2 months ago. The current meteoric rise have been possible because it was an unregulated wild wild west. The reason Ethereum was able to avoid dropping compared to other cryptos recently was because there was a positive development announced by the Ethereum Foundation. That's about a scaling solution called Sharding. But while progress is definite, its been coming in at a steady pace. Such announcements may only hold Ethereum from dropping further, rather than prompting another crazy rise.
The reason is because the trend towards cryptos have changed. It'll get rid of the underground, dark web style of people, it'll get rid of the absolutely newbie investors, it'll get rid of those that do it to avoid government intervention(like for paying taxes). That's likely a nontrivial amount of "investors" at the moment.
It won't go up at this rate forever. While its true investing is driven primarily by emotions, it can be argued some logical analysis does happen. When EF successfully scales Ethereum to be "visa-like" in amount of transactions it can handle, when EF successfully implements PoS, then it can start moving to a more mature phase where real world applications start to appear.
Then, maybe it can reach the point of ubiquity. Then $5K starts making sense. It may take a decade.