Ethereum could never be the second btc. Even the forked version of bitcoin cannot cope up with the bitcoin's market pace. But I am not criticizing Ethereum since it has a big future but compared to bitcoin it can never surpassed it. Ethereum could also be a big hit and will join the wave of bitcoin's market. As long as bitcoin goes up then so as Ethereum.
It already is second to BTC if you just look at the ranks of the coinmarketcap. Prices differ though but it won't take long I think ETH will also rise up and will be worth more than $1000. The possibility of a coin to dominate the first over BTC might happen one day and if it isn't ETH, it could be NEO which is much sophisticated platform than ETH.