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).
Maybe we can consider the King to be the highest market cap. If so, I don't think any other crypto can surpass Eth and Bitcoin in 2018.
I also think the only big contestant to Bitcoin in 2018 is Ethereum. Perhaps it can reach the highest market cap till the end of the year. Specially considering the recent Eth rally.