Will another coin beat bitcoin in terms of total market cap? Maybe, maybe not. Is it possible? Very possible. Though Ethereum is slowly but surely closing up on market cap(currently a 57.3 billion difference[1]), it still has a far far way to go; and I honestly don't see bitcoin being replaced soon. Probably in the future, but who knows? Too early to tell. And it might not even be ETH.
[1]
https://coinmarketcap.com/yes i agree that eth is just one among many to beat bitcoin. and these talks are quite often in here, because we see that both alts and btc need some improvements. what if we mix it? there will be a perfect duo