Right now the prices of all altcoin in very drastic, especially ETH, whether in 2019 it'll be back, or just keep it stable?
Give me your opinion.
The ether team began work in 2019 badly. They will not launch Constantinople in any way and this only aggravates the situation. If Constantinople is successfully launched, the price of the ether will grow.
As for the other altcoins, they simply follows bitcoin. If Bakkt is approved in the spring, then we should expect a rise in the price of bitcoin, and accordingly on the rest of the altcoins.
In general, I think that the year 2019 will be relatively stable, but in the autumn I expect a significant increase in prices.