As you can see, from Fibonacci, ETH price still has lot's of room for a retracement downward, before forming a new uptrend wave.
If the price retraces at the golden level, then expect the price to reach 540, before turning into an uptrend.
By 2019, this is going to be the lowest point to buy, since I don't think ETH will ever reach again the 500 area. By December, ETH should be above 1,000