How long until this happens?
This is not possible at current cycle conditions. Though the volatility at the end of 2020 is huge. The total supply of ETH is nearly 7 times that of bitcoin. In contrast, bitcoin's value hit a staggering 26 times the value of ETH. Looking back, in 2017 the Bitcoin and ETH gap was 14 times. This gap is getting bigger. This proves, bitcoin is irreplaceable. And thus, an impossible task for ETH.