I don't think that anything should replace Bitcoin. Bitcoin is the leader of crypto and the flagman for the whole industry IMO.
I do not think there is any coin to replace the BTC in the future, I believe the BTC is the king of the Crypto market forever, even if the market is falling, BTC is still a coin occupied. By the end of 2018, BTC prices will rise more than $ 50,000. I believe this will happen.
In my opinion, there can be no other crypto coin amongst all the crypto coins which are there in the world of the crypto currencies which have this much of the potential and the capabilities that any of them can replace the bitcoin even after so many years from now as well. It is because bitcoin is the only coin on which the entire foundation of the crypto currencies is being laid and that place cannot be taken by any other coin.