I think this will never happen. Bitcoin is the king of all the coins. It has great value. Bitcoin has gone through many challenges, to survive to the present. Bitcoin is trusted by many investors. It is very difficult for the altcoin to turn a bitcoin.
Ofcourse, I too believe it is not so easy to replace BTC by any altcoin but there were more predictions of ETH as it will beat BTC these two coins are very popular in the crypto market and eth is a good competitor for BTC as well. Lets wait and watch how things work in the future.