No one will dethrone BitCoin form being the king of crypto!
But, IMO, 2018 will be the year of some already successfull altcoins like Ethereum or Cardano
and we should keep an eye on interesting project like DeepOnion or KIN

It is going to be like trying to do something that is totally not possible.
Yes, we could say anything is possible in the crypto world but there are somethings that just do not sound like it. I have seen some people using market cap to judge the fact that ripple is taking over bitcoin, when market cap can easily be manipulated, most especially for a centralized coin, it would even be a matter of time before XRP get bounced back.