It is impossible and will not happen, I myself do not find a factor to strengthen the statement that Cardano is able to overthrow ETH, maybe the cost problem at ETH has not been resolved, but some time ago the cost of ETH was cheap. ETH has come up with an innovative design to solve this problem and let's see how powerful ETH is.
The cost is not the solely thing that matters. Ethereum smart contracts can not be mathematically checked. That is why they can contain errors that in might result in hacks and money lost. This is not apply to smart contracts to be developed on Cardano. They can be strongly checked and proved using the methods of pure mathematics.