In my opinion, ETH will be number2 coin,not second BTC, bitcoin is bitcoin and no one can replace bitcoiN as number 1 in cryptocurrency, although yes eth is also a good coin but it cant take the place of btc on top.
Sure bitcoin will always remain the first cryptocurrency, but ethereum to me will remain the best cryptocurrency. So many use cases, the smart contract ethereum offers alone has place it on a pedestal that bitcoin can never attain.
I think Ethereum is fighting for a position with Bitcoin for a long time because I know with the fighting of Ethereum and bitcoin ago because Ethereum has better growth than Bitcoin so Ethereum dare to take Bitcoin's position but even so Bitcoin cannot possibly be replaced