No hesitation bitcoin will always be the king for 2018 and in the coming years. As you see the market everytime bitcoin drops its value all altcoins follow.
In my opinion, Bitcoin would still be the king of all crypto currencies. It has become the trademark of crypto itself. When you talk to some stranger about crypto currency, the first thing that will pop out of their mind will be Bitcoin. The popularity of Bitcoin is comparable to a God in a religion.
It depends on what is meant by King; if by Re author thread intends percentage growth then bitcoin probably will not be the King in 2018, just as it was not in 2017 (about x10 while about x100 about Xrp and Eth).
The growth in listing is very different from the growth and adoption of mainstream, from its use and real use in the real world.
The popularity and the brand as someone says can always change or be lost, just as its dominance is falling; one day the other coins will no longer be coupled to the exchange rate in Btc and will no longer have all this correspondence with it.