I think it's very difficult to happen because until now Ethereum continues to experience price increases and I am sure ETH will reach the price of $ 700 at the end of 2018,
It is possible because anything can happen to a crypto even how strong and dominant it is because of its volatility of its price. Glad to see that Ethereum is holding on and still keeps hovering in the 400$ mark but touching down 300$ is really possible.